136 lines
2.6 KiB
Java
136 lines
2.6 KiB
Java
package DataStructures.Stacks;
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import java.util.NoSuchElementException;
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/** @author Varun Upadhyay (https://github.com/varunu28) */
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// An implementation of a Stack using a Linked List
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class StackOfLinkedList {
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public static void main(String[] args) {
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LinkedListStack stack = new LinkedListStack();
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stack.push(1);
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stack.push(2);
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stack.push(3);
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stack.push(4);
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stack.push(5);
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System.out.println(stack);
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System.out.println("Size of stack currently is: " + stack.getSize());
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assert stack.pop() == 5;
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assert stack.pop() == 4;
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System.out.println("Top element of stack currently is: " + stack.peek());
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}
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}
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// A node class
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class Node {
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public int data;
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public Node next;
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public Node(int data) {
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this.data = data;
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this.next = null;
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}
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}
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/**
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* A class which implements a stack using a linked list
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*
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* <p>Contains all the stack methods : push, pop, printStack, isEmpty
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*/
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class LinkedListStack {
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/** Top of stack */
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Node head;
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/** Size of stack */
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private int size;
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/** Init properties */
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public LinkedListStack() {
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head = null;
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size = 0;
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}
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/**
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* Add element at top
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*
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* @param x to be added
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* @return <tt>true</tt> if add successfully
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*/
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public boolean push(int x) {
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Node newNode = new Node(x);
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newNode.next = head;
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head = newNode;
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size++;
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return true;
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}
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/**
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* Pop element at top of stack
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*
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* @return element at top of stack
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* @throws NoSuchElementException if stack is empty
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*/
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public int pop() {
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if (size == 0) {
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throw new NoSuchElementException("Empty stack. Nothing to pop");
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}
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Node destroy = head;
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head = head.next;
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int retValue = destroy.data;
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destroy = null; // clear to let GC do it's work
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size--;
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return retValue;
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}
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/**
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* Peek element at top of stack
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*
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* @return element at top of stack
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* @throws NoSuchElementException if stack is empty
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*/
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public int peek() {
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if (size == 0) {
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throw new NoSuchElementException("Empty stack. Nothing to pop");
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}
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return head.data;
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}
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@Override
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public String toString() {
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Node cur = head;
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StringBuilder builder = new StringBuilder();
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while (cur != null) {
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builder.append(cur.data).append("->");
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cur = cur.next;
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}
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return builder.replace(builder.length() - 2, builder.length(), "").toString();
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}
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/**
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* Check if stack is empty
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*
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* @return <tt>true</tt> if stack is empty, otherwise <tt>false</tt>
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*/
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public boolean isEmpty() {
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return size == 0;
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}
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/**
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* Return size of stack
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*
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* @return size of stack
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*/
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public int getSize() {
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return size;
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}
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}
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