refactor: HashMap (#5426)
* refactor: HashMap * checkstyle: fix formatting * refactor: remove redundant comments --------- Co-authored-by: alxkm <alx@alx.com>
This commit is contained in:
Alex Klymenko
GitHub
parent
6b7a1fdbe8
commit
a23e9b0ba8
@ -1,146 +1,275 @@
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package com.thealgorithms.datastructures.hashmap.hashing;
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package com.thealgorithms.datastructures.hashmap.hashing;
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public class HashMap {
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/**
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* A generic HashMap implementation that uses separate chaining with linked lists
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* to handle collisions. The class supports basic operations such as insert, delete,
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* and search, as well as displaying the contents of the hash map.
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*
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* @param <K> the type of keys maintained by this map
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* @param <V> the type of mapped values
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*/
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public class HashMap<K, V> {
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private final int hashSize;
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private final LinkedList<K, V>[] buckets;
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private final int hsize;
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/**
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private final LinkedList[] buckets;
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* Constructs a HashMap with the specified hash size.
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*
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public HashMap(int hsize) {
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* @param hashSize the number of buckets in the hash map
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buckets = new LinkedList[hsize];
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*/
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for (int i = 0; i < hsize; i++) {
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@SuppressWarnings("unchecked")
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buckets[i] = new LinkedList();
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public HashMap(int hashSize) {
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// Java requires explicit initialization of each object
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this.hashSize = hashSize;
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// Safe to suppress warning because we are creating an array of generic type
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this.buckets = new LinkedList[hashSize];
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for (int i = 0; i < hashSize; i++) {
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buckets[i] = new LinkedList<>();
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}
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}
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this.hsize = hsize;
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}
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}
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public int hashing(int key) {
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/**
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int hash = key % hsize;
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* Computes the hash code for the specified key.
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if (hash < 0) {
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* Null keys are hashed to bucket 0.
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hash += hsize;
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*
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* @param key the key for which the hash code is to be computed
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* @return the hash code corresponding to the key
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*/
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private int computeHash(K key) {
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if (key == null) {
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return 0; // Use a special bucket (e.g., bucket 0) for null keys
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}
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}
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return hash;
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int hash = key.hashCode() % hashSize;
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return hash < 0 ? hash + hashSize : hash;
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}
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}
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public void insertHash(int key) {
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/**
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int hash = hashing(key);
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* Inserts the specified key-value pair into the hash map.
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buckets[hash].insert(key);
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* If the key already exists, the value is updated.
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*
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* @param key the key to be inserted
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* @param value the value to be associated with the key
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*/
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public void insert(K key, V value) {
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int hash = computeHash(key);
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buckets[hash].insert(key, value);
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}
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}
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public void deleteHash(int key) {
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/**
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int hash = hashing(key);
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* Deletes the key-value pair associated with the specified key from the hash map.
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*
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* @param key the key whose key-value pair is to be deleted
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*/
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public void delete(K key) {
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int hash = computeHash(key);
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buckets[hash].delete(key);
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buckets[hash].delete(key);
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}
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}
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public void displayHashtable() {
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/**
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for (int i = 0; i < hsize; i++) {
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* Searches for the value associated with the specified key in the hash map.
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System.out.printf("Bucket %d :", i);
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*
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System.out.println(buckets[i].display());
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* @param key the key whose associated value is to be returned
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* @return the value associated with the specified key, or null if the key does not exist
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*/
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public V search(K key) {
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int hash = computeHash(key);
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Node<K, V> node = buckets[hash].findKey(key);
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return node != null ? node.getValue() : null;
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}
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/**
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* Displays the contents of the hash map, showing each bucket and its key-value pairs.
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*/
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public void display() {
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for (int i = 0; i < hashSize; i++) {
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System.out.printf("Bucket %d: %s%n", i, buckets[i].display());
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}
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}
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}
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}
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public static class LinkedList {
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/**
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* A nested static class that represents a linked list used for separate chaining in the hash map.
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*
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* @param <K> the type of keys maintained by this linked list
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* @param <V> the type of mapped values
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*/
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public static class LinkedList<K, V> {
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private Node<K, V> head;
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private Node first;
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/**
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* Inserts the specified key-value pair into the linked list.
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public LinkedList() {
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* If the linked list is empty, the pair becomes the head.
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first = null;
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* Otherwise, the pair is added to the end of the list.
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}
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*
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* @param key the key to be inserted
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public void insert(int key) {
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* @param value the value to be associated with the key
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if (isEmpty()) {
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*/
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first = new Node(key);
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public void insert(K key, V value) {
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return;
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Node<K, V> existingNode = findKey(key);
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if (existingNode != null) {
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existingNode.setValue(value); // Update the value, even if it's null
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} else {
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if (isEmpty()) {
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head = new Node<>(key, value);
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} else {
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Node<K, V> temp = findEnd(head);
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temp.setNext(new Node<>(key, value));
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}
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}
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}
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Node temp = findEnd(first);
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temp.setNext(new Node(key));
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}
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}
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private Node findEnd(Node n) {
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/**
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while (n.getNext() != null) {
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* Finds the last node in the linked list.
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n = n.getNext();
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*
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* @param node the starting node
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* @return the last node in the linked list
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*/
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private Node<K, V> findEnd(Node<K, V> node) {
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while (node.getNext() != null) {
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node = node.getNext();
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}
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}
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return n;
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return node;
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}
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}
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public Node findKey(int key) {
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/**
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if (!isEmpty()) {
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* Finds the node associated with the specified key in the linked list.
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Node temp = first;
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*
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if (temp.getKey() == key) {
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* @param key the key to search for
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* @return the node associated with the specified key, or null if not found
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*/
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public Node<K, V> findKey(K key) {
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Node<K, V> temp = head;
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while (temp != null) {
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if ((key == null && temp.getKey() == null) || (temp.getKey() != null && temp.getKey().equals(key))) {
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return temp;
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return temp;
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}
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}
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temp = temp.getNext();
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while ((temp = temp.getNext()) != null) {
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if (temp.getKey() == key) {
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return temp;
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}
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}
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}
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}
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return null;
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return null;
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}
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}
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public void delete(int key) {
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/**
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if (!isEmpty()) {
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* Deletes the node associated with the specified key from the linked list.
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if (first.getKey() == key) {
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* Handles the case where the key could be null.
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Node next = first.next;
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*
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first.next = null; // help GC
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* @param key the key whose associated node is to be deleted
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first = next;
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*/
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} else {
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public void delete(K key) {
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delete(first, key);
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if (isEmpty()) {
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return;
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}
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// Handle the case where the head node has the key to delete
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if ((key == null && head.getKey() == null) || (head.getKey() != null && head.getKey().equals(key))) {
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head = head.getNext();
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return;
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}
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// Traverse the list to find and delete the node
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Node<K, V> current = head;
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while (current.getNext() != null) {
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if ((key == null && current.getNext().getKey() == null) || (current.getNext().getKey() != null && current.getNext().getKey().equals(key))) {
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current.setNext(current.getNext().getNext());
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return;
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}
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}
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current = current.getNext();
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}
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}
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}
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}
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private void delete(Node n, int key) {
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/**
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if (n.getNext().getKey() == key) {
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* Displays the contents of the linked list as a string.
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if (n.getNext().getNext() == null) {
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*
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n.setNext(null);
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* @return a string representation of the linked list
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} else {
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*/
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n.setNext(n.getNext().getNext());
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}
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} else {
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delete(n.getNext(), key);
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}
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}
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public String display() {
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public String display() {
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return display(first);
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return display(head);
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}
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}
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private String display(Node n) {
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/**
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if (n == null) {
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* Constructs a string representation of the linked list non-recursively.
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return "null";
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*
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} else {
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* @param node the starting node
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return n.getKey() + "->" + display(n.getNext());
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* @return a string representation of the linked list starting from the given node
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*/
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private String display(Node<K, V> node) {
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StringBuilder sb = new StringBuilder();
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while (node != null) {
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sb.append(node.getKey()).append("=").append(node.getValue());
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node = node.getNext();
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if (node != null) {
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sb.append(" -> ");
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}
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}
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}
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return sb.toString().isEmpty() ? "null" : sb.toString();
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}
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}
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/**
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* Checks if the linked list is empty.
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*
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* @return true if the linked list is empty, false otherwise
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*/
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public boolean isEmpty() {
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public boolean isEmpty() {
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return first == null;
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return head == null;
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}
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}
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}
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}
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public static class Node {
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/**
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* A nested static class representing a node in the linked list.
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*
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* @param <K> the type of key maintained by this node
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* @param <V> the type of value maintained by this node
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*/
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public static class Node<K, V> {
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private final K key;
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private V value;
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private Node<K, V> next;
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private Node next;
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/**
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private final int key;
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* Constructs a Node with the specified key and value.
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*
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public Node(int key) {
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* @param key the key associated with this node
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next = null;
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* @param value the value associated with this node
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*/
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public Node(K key, V value) {
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this.key = key;
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this.key = key;
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this.value = value;
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}
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}
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public Node getNext() {
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/**
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return next;
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* Gets the key associated with this node.
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}
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*
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* @return the key associated with this node
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public int getKey() {
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*/
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public K getKey() {
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return key;
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return key;
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}
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}
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public void setNext(Node next) {
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/**
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* Gets the value associated with this node.
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*
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* @return the value associated with this node
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*/
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public V getValue() {
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return value;
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}
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public void setValue(V value) { // This method allows updating the value
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this.value = value;
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}
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/**
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* Gets the next node in the linked list.
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*
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* @return the next node in the linked list
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*/
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public Node<K, V> getNext() {
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return next;
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}
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/**
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* Sets the next node in the linked list.
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*
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* @param next the next node to be linked
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*/
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public void setNext(Node<K, V> next) {
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this.next = next;
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this.next = next;
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}
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}
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}
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}
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@ -1,52 +0,0 @@
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package com.thealgorithms.datastructures.hashmap.hashing;
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import java.util.Scanner;
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public final class Main {
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private Main() {
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}
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public static void main(String[] args) {
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int choice;
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int key;
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HashMap h = new HashMap(7);
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Scanner scan = new Scanner(System.in);
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while (true) {
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System.out.println("Enter your Choice :");
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System.out.println("1. Add Key");
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System.out.println("2. Delete Key");
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System.out.println("3. Print Table");
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System.out.println("4. Exit");
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choice = scan.nextInt();
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switch (choice) {
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case 1:
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System.out.println("Enter the Key: ");
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key = scan.nextInt();
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h.insertHash(key);
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break;
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case 2:
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System.out.println("Enter the Key delete: ");
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key = scan.nextInt();
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h.deleteHash(key);
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break;
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case 3:
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System.out.println("Print table");
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h.displayHashtable();
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break;
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case 4:
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scan.close();
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return;
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default:
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throw new IllegalArgumentException("Unexpected value: " + choice);
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}
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}
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}
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}
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@ -0,0 +1,146 @@
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package com.thealgorithms.datastructures.hashmap.hashing;
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import static org.junit.jupiter.api.Assertions.assertEquals;
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import static org.junit.jupiter.api.Assertions.assertNull;
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import org.junit.jupiter.api.Test;
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public class HashMapTest {
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@Test
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public void testInsertAndSearch() {
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HashMap<Integer, String> hashMap = new HashMap<>(10);
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hashMap.insert(15, "Value15");
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hashMap.insert(25, "Value25");
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hashMap.insert(35, "Value35");
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assertEquals("Value15", hashMap.search(15));
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assertEquals("Value25", hashMap.search(25));
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assertEquals("Value35", hashMap.search(35));
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assertNull(hashMap.search(45));
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}
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@Test
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public void testDelete() {
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HashMap<Integer, String> hashMap = new HashMap<>(10);
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hashMap.insert(15, "Value15");
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hashMap.insert(25, "Value25");
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hashMap.insert(35, "Value35");
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assertEquals("Value25", hashMap.search(25));
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hashMap.delete(25);
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assertNull(hashMap.search(25));
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}
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@Test
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public void testDisplay() {
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||||||
|
HashMap<Integer, String> hashMap = new HashMap<>(5);
|
||||||
|
hashMap.insert(15, "Value15");
|
||||||
|
hashMap.insert(25, "Value25");
|
||||||
|
hashMap.insert(35, "Value35");
|
||||||
|
hashMap.display();
|
||||||
|
}
|
||||||
|
|
||||||
|
@Test
|
||||||
|
public void testInsertNullKey() {
|
||||||
|
HashMap<Integer, String> hashMap = new HashMap<>(10);
|
||||||
|
hashMap.insert(null, "NullValue");
|
||||||
|
assertEquals("NullValue", hashMap.search(null));
|
||||||
|
}
|
||||||
|
|
||||||
|
@Test
|
||||||
|
public void testInsertNullValue() {
|
||||||
|
HashMap<Integer, String> hashMap = new HashMap<>(10);
|
||||||
|
hashMap.insert(15, null);
|
||||||
|
assertNull(hashMap.search(15));
|
||||||
|
}
|
||||||
|
|
||||||
|
@Test
|
||||||
|
public void testUpdateExistingKey() {
|
||||||
|
HashMap<Integer, String> hashMap = new HashMap<>(10);
|
||||||
|
hashMap.insert(15, "Value15");
|
||||||
|
hashMap.insert(15, "UpdatedValue15");
|
||||||
|
|
||||||
|
assertEquals("UpdatedValue15", hashMap.search(15));
|
||||||
|
}
|
||||||
|
|
||||||
|
@Test
|
||||||
|
public void testHandleCollisions() {
|
||||||
|
HashMap<Integer, String> hashMap = new HashMap<>(3);
|
||||||
|
// These keys should collide if the hash function is modulo 3
|
||||||
|
hashMap.insert(1, "Value1");
|
||||||
|
hashMap.insert(4, "Value4");
|
||||||
|
hashMap.insert(7, "Value7");
|
||||||
|
|
||||||
|
assertEquals("Value1", hashMap.search(1));
|
||||||
|
assertEquals("Value4", hashMap.search(4));
|
||||||
|
assertEquals("Value7", hashMap.search(7));
|
||||||
|
}
|
||||||
|
|
||||||
|
@Test
|
||||||
|
public void testSearchInEmptyHashMap() {
|
||||||
|
HashMap<Integer, String> hashMap = new HashMap<>(10);
|
||||||
|
assertNull(hashMap.search(10));
|
||||||
|
}
|
||||||
|
|
||||||
|
@Test
|
||||||
|
public void testDeleteNonExistentKey() {
|
||||||
|
HashMap<Integer, String> hashMap = new HashMap<>(10);
|
||||||
|
hashMap.insert(15, "Value15");
|
||||||
|
hashMap.delete(25);
|
||||||
|
|
||||||
|
assertEquals("Value15", hashMap.search(15));
|
||||||
|
assertNull(hashMap.search(25));
|
||||||
|
}
|
||||||
|
|
||||||
|
@Test
|
||||||
|
public void testInsertLargeNumberOfElements() {
|
||||||
|
HashMap<Integer, String> hashMap = new HashMap<>(10);
|
||||||
|
for (int i = 0; i < 100; i++) {
|
||||||
|
hashMap.insert(i, "Value" + i);
|
||||||
|
}
|
||||||
|
|
||||||
|
for (int i = 0; i < 100; i++) {
|
||||||
|
assertEquals("Value" + i, hashMap.search(i));
|
||||||
|
}
|
||||||
|
}
|
||||||
|
|
||||||
|
@Test
|
||||||
|
public void testDeleteHeadOfBucket() {
|
||||||
|
HashMap<Integer, String> hashMap = new HashMap<>(3);
|
||||||
|
hashMap.insert(1, "Value1");
|
||||||
|
hashMap.insert(4, "Value4");
|
||||||
|
hashMap.insert(7, "Value7");
|
||||||
|
|
||||||
|
hashMap.delete(1);
|
||||||
|
assertNull(hashMap.search(1));
|
||||||
|
assertEquals("Value4", hashMap.search(4));
|
||||||
|
assertEquals("Value7", hashMap.search(7));
|
||||||
|
}
|
||||||
|
|
||||||
|
@Test
|
||||||
|
public void testDeleteTailOfBucket() {
|
||||||
|
HashMap<Integer, String> hashMap = new HashMap<>(3);
|
||||||
|
hashMap.insert(1, "Value1");
|
||||||
|
hashMap.insert(4, "Value4");
|
||||||
|
hashMap.insert(7, "Value7");
|
||||||
|
|
||||||
|
hashMap.delete(7);
|
||||||
|
assertNull(hashMap.search(7));
|
||||||
|
assertEquals("Value1", hashMap.search(1));
|
||||||
|
assertEquals("Value4", hashMap.search(4));
|
||||||
|
}
|
||||||
|
|
||||||
|
@Test
|
||||||
|
public void testDeleteMiddleElementOfBucket() {
|
||||||
|
HashMap<Integer, String> hashMap = new HashMap<>(3);
|
||||||
|
hashMap.insert(1, "Value1");
|
||||||
|
hashMap.insert(4, "Value4");
|
||||||
|
hashMap.insert(7, "Value7");
|
||||||
|
|
||||||
|
hashMap.delete(4);
|
||||||
|
assertNull(hashMap.search(4));
|
||||||
|
assertEquals("Value1", hashMap.search(1));
|
||||||
|
assertEquals("Value7", hashMap.search(7));
|
||||||
|
}
|
||||||
|
}
|
||||||
Loading…
Reference in New Issue
Block a user