JavaAlgorithms/DataStructures/Lists/SinglyLinkedList.java

package DataStructures.Lists;

import java.util.StringJoiner;

/** https://en.wikipedia.org/wiki/Linked_list */
public class SinglyLinkedList {
  /** Head refer to the front of the list */
  private Node head;

  /** Size of SinglyLinkedList */
  private int size;

  /** Init SinglyLinkedList */
  public SinglyLinkedList() {
    head = null;
    size = 0;
  }

  /**
   * Init SinglyLinkedList with specified head node and size
   *
   * @param head the head node of list
   * @param size the size of list
   */
  public SinglyLinkedList(Node head, int size) {
    this.head = head;
    this.size = size;
  }

  /**
   * Inserts an element at the head of the list
   *
   * @param x element to be added
   */
  public void insertHead(int x) {
    insertNth(x, 0);
  }

  /**
   * Insert an element at the tail of the list
   *
   * @param data element to be added
   */
  public void insert(int data) {
    insertNth(data, size);
  }

  /**
   * Inserts a new node at a specified position of the list
   *
   * @param data data to be stored in a new node
   * @param position position at which a new node is to be inserted
   */
  public void insertNth(int data, int position) {
    checkBounds(position, 0, size);
    Node newNode = new Node(data);
    if (head == null) {
      /* the list is empty */
      head = newNode;
      size++;
      return;
    } else if (position == 0) {
      /* insert at the head of the list */
      newNode.next = head;
      head = newNode;
      size++;
      return;
    }
    Node cur = head;
    for (int i = 0; i < position - 1; ++i) {
      cur = cur.next;
    }
    newNode.next = cur.next;
    cur.next = newNode;
    size++;
  }

  /** Deletes a node at the head */
  public void deleteHead() {
    deleteNth(0);
  }

  /** Deletes an element at the tail */
  public void delete() {
    deleteNth(size - 1);
  }

  /** Deletes an element at Nth position */
  public void deleteNth(int position) {
    checkBounds(position, 0, size - 1);
    if (position == 0) {
      Node destroy = head;
      head = head.next;
      destroy = null; /* clear to let GC do its work */
      size--;
      return;
    }
    Node cur = head;
    for (int i = 0; i < position - 1; ++i) {
      cur = cur.next;
    }

    Node destroy = cur.next;
    cur.next = cur.next.next;
    destroy = null; // clear to let GC do its work

    size--;
  }

  /**
   * @param position to check position
   * @param low low index
   * @param high high index
   * @throws IndexOutOfBoundsException if {@code position} not in range {@code low} to {@code high}
   */
  public void checkBounds(int position, int low, int high) {
    if (position > high || position < low) {
      throw new IndexOutOfBoundsException(position + "");
    }
  }

  /** Clear all nodes in the list */
  public void clear() {
    Node cur = head;
    while (cur != null) {
      Node prev = cur;
      cur = cur.next;
      prev = null; // clear to let GC do its work
    }
    head = null;
    size = 0;
  }

  /**
   * Checks if the list is empty
   *
   * @return {@code true} if list is empty, otherwise {@code false}.
   */
  public boolean isEmpty() {
    return size == 0;
  }

  /**
   * Returns the size of the linked list.
   *
   * @return the size of the list.
   */
  public int size() {
    return size;
  }

  /**
   * Get head of the list.
   *
   * @return head of the list.
   */
  public Node getHead() {
    return head;
  }

  /**
   * Calculate the count of the list manually
   *
   * @return count of the list
   */
  public int count() {
    int count = 0;
    Node cur = head;
    while (cur != null) {
      cur = cur.next;
      count++;
    }
    return count;
  }

  /**
   * Test if the value key is present in the list.
   *
   * @param key the value to be searched.
   * @return {@code true} if key is present in the list, otherwise {@code false}.
   */
  public boolean search(int key) {
    Node cur = head;
    while (cur != null) {
      if (cur.value == key) {
        return true;
      }
      cur = cur.next;
    }
    return false;
  }

  /**
   * Return element at special index.
   *
   * @param index given index of element
   * @return element at special index.
   */
  public int getNth(int index) {
    checkBounds(index, 0, size - 1);
    Node cur = head;
    for (int i = 0; i < index; ++i) {
      cur = cur.next;
    }
    return cur.value;
  }

  @Override
  public String toString() {
    StringJoiner joiner = new StringJoiner("->");
    Node cur = head;
    while (cur != null) {
      joiner.add(cur.value + "");
      cur = cur.next;
    }
    return joiner.toString();
  }

  /** Driver Code */
  public static void main(String[] arg) {
    SinglyLinkedList list = new SinglyLinkedList();
    assert list.isEmpty();
    assert list.size() == 0 && list.count() == 0;
    assert list.toString().equals("");

    /* Test insert function */
    list.insertHead(5);
    list.insertHead(7);
    list.insertHead(10);
    list.insert(3);
    list.insertNth(1, 4);
    assert list.toString().equals("10->7->5->3->1");

    /* Test search function */
    assert list.search(10) && list.search(5) && list.search(1) && !list.search(100);

    /* Test get function */
    assert list.getNth(0) == 10 && list.getNth(2) == 5 && list.getNth(4) == 1;

    /* Test delete function */
    list.deleteHead();
    list.deleteNth(1);
    list.delete();
    assert list.toString().equals("7->3");

    assert list.size == 2 && list.size() == list.count();

    list.clear();
    assert list.isEmpty();

    try {
      list.delete();
      assert false; /* this should not happen */
    } catch (Exception e) {
      assert true; /* this should happen */
    }
  }
}

/**
 * This class is the nodes of the SinglyLinked List. They consist of a value and a pointer to the
 * node after them.
 */
class Node {
  /** The value of the node */
  int value;

  /** Point to the next node */
  Node next;

  Node() {}

  /**
   * Constructor
   *
   * @param value Value to be put in the node
   */
  Node(int value) {
    this(value, null);
  }

  /**
   * Constructor
   *
   * @param value Value to be put in the node
   * @param next Reference to the next node
   */
  Node(int value, Node next) {
    this.value = value;
    this.next = next;
  }
}