leetcode/lcci/02.01.Remove Duplicate Node/Solution.java

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode removeDuplicateNodes(ListNode head) {
        Set<Integer> vis = new HashSet<>();
        ListNode pre = new ListNode(0, head);
        while (pre.next != null) {
            if (vis.add(pre.next.val)) {
                pre = pre.next;
            } else {
                pre.next = pre.next.next;
            }
        }
        return head;
    }
}