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82. Remove Duplicates from Sorted List II

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

Example 1:

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Input: head = [1,2,3,3,4,4,5]
Output: [1,2,5]

Example 2:

img

Input: head = [1,1,1,2,3]
Output: [2,3]

Constraints:

  • The number of nodes in the list is in the range [0, 300].
  • -100 <= Node.val <= 100
  • The list is guaranteed to be sorted in ascending order.

Solution:

/**
 * 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 dummy = new ListNode(-1);
        dummy.next = head;
        ListNode cur = dummy;

        while(cur.next != null && cur.next.next != null){
            int val = cur.next.val;

            if (cur.next.next.val == val){
                while(cur.next != null && cur.next.val == val){
                    cur.next =cur.next.next;
                }
            }else{
                cur =cur.next;
            }
        }
        return dummy.next;
    }
}


// TC: O(n)
// SC: O(1)