Remove Duplicates from Sorted List

Leetcode 83.

version 1

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/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode deleteDuplicates(ListNode head) {
      ListNode temp = head;
      while(temp != null && temp.next != null){
        if(temp.val == temp.next.val){
            temp.next = temp.next.next; 
        } 
        if(temp.next != null && temp.val != temp.next.val)
           temp = temp.next;
      }
     return head;
    }
}

version 2 Recursion

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/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode deleteDuplicates(ListNode head) {
     if(head == null || head.next == null){
         return head;
     }
    head.next = deleteDuplicates(head.next); 
    return head.val == head.next.val ? head.next : head;    
   }
}