Leetcode–Remove Duplicates from Sorted List

The Problem:

Given a sorted linked list, delete all duplicates such that each element appear only once.

For example,
Given 1->1->2, return 1->2.
Given 1->1->2->3->3, return 1->2->3.

Notes:

  1. Keep track of previous node rather than just the node value, so will be convenient when deleting current node.
  2. When the current node is deleted, current node should point to previous one rather than next one.

Java Solution:

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode deleteDuplicates(ListNode head) {
        if(head==null || head.next==null)
            return head;
        ListNode prev = head;
        ListNode p = head;
        while(p.next!=null){
            p = p.next;
            if(p.val == prev.val){
                prev.next = p.next;
                p.next = null;
                p = prev;
            }
            else{
                prev = p;
            }
        }
        return head;
    }
}
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