[Leetcode]82. Remove Duplicates from Sorted List II

Question

Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.

For example,

For example,
Given 1->2->3->3->4->4->5, return 1->2->5.

For example,
Given 1->2->3->3->4->4->5, return 1->2->5.
Given 1->1->1->2->3, return 2->3.

Solution

Because the head of linked list could be duplicated, so we need to add a dummy head node to the original linked list. Then check the values of node, if it’s duplicated just skip the node and redirect the pointer to next node.

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode deleteDuplicates(ListNode head) {
        if( head == null || head.next == null ){      //edge case
            return head;
        }
        ListNode ret = new ListNode(0);               // fake head 
        ret.next = head;
        head = ret;
        while(head.next != null && head.next.next != null){  // start checking
            if(head.next.val == head.next.next.val){
                int value = head.next.val;
                while( head.next != null && head.next.val == value ){ 
                    head.next = head.next.next;      //redirect head's next pointer
                }
            }else{
                head = head.next;                  //head move to next node
            }
        }
        
        return  ret.next;
        
    }
}