LinkedList Class

/**
 *  Homework 09 - Linked List
 *
 *   *
 *  Prompt:    Create a LinkedList class
 *
 *             The LinkedList class should contain the following public
 *             properties:
 *
 *                length:   {Integer}
 *                  head:   {ListNode}
 *                  tail:   {ListNode}
 *
 *              The LinkedList class should also contain the following public
 *              methods:
 *
 *                append:   A method that appends a value to the end of the
 *                          LinkedList.
 *
 *                          Input:     {Integer}
 *                          Output:    {Void}
 *
 *                insert:   A method that inserts an integer value at a set
 *                          index in the LinkedList (assume head index is 0).
 *
 *                          Input:     value {Integer}
 *                          Input:     index {Integer}
 *                          Output:    {Void}
 *
 *                delete:   A method that removes a node at a specified index.
 *
 *                          Input:     index {Integer}
 *                          Output:    {Void}
 *
 *              contains:   A method that checks to see if a value is contained
 *                          in the list.
 *
 *                          Input:     value {Integer}
 *                          Output:    {Boolean}
 */

import java.util.*;

class ListNode {
  public int value;
  public ListNode next;

  public ListNode(int value){
    this.value = value;
    this.next = null;
  }
}


class LinkedList {
  public int length = 0;
  public ListNode head;
  public ListNode tail;

  // Time Complexity:
  // Auxiliary Space Complexity:
  public void append(int value){
    insert(value, length);
  }


  // Time Complexity:
  // Auxiliary Space Complexity:
  public void insert(int value, int index){
    //check to see if index for insertion is out of bounds of the LinkedList
    if(index > length || index < 0){
      return;
    }
    ListNode newNode = new ListNode(value);
    //if no nodes exist, new node is head AND tail
    if(length == 0){
      head = newNode;
      tail = newNode;
    }else if(index == 0){
      //set new node to pt to curr head next
      //set head to pt to new node
      newNode.next = head;
      head = newNode;
    }else if(index == length){
      tail.next = newNode;
      tail = newNode;
    }else{
      //if inserting somewhere in the middle->
      //make iterator node variable and set to head of LinkedList
      ListNode previousNode = head;
      for(int i = 0; i< index-1; i++){
        previousNode = previousNode.next;
      }
      //once node previous to index, insert newNode
      newNode.next = previousNode.next;
      previousNode.next = newNode;
    }
    //increase length to acct for inserted node
    length++;
  }


   // Time Complexity: O(N)
  // Auxiliary Space Complexity: O(1)
   public void delete(int index){

    //out of bounds? return
    if(index < 0 || index >= length){
      return;
    }
    //if there is only 1 item in LinkedList
    if(length == 1){
      head = null;
      tail = null;
    }else if(index == 0){
      head = head.next;
    }else {
      //create iterator
      ListNode previousNode = head;
      for(int i = 0 ; i <index-1; i++){
        previousNode = previousNode.next;
      }
      previousNode.next = previousNode.next.next;
      if(index == length -1){
        tail = previousNode;
      }
    }
    length--;
  }


  // Time Complexity: O(N)
  // Auxiliary Space Complexity:O(1)
  public boolean contains(int value){
      //create iterator for search
      ListNode currNode = head;
      for(int i = 0; i < length; i++){
        if(currNode.value == value){
          return true;
        }else{
          currNode = currNode.next;
        }
      }
      return false;
   }
}