移除重复节点

/*
 * 思路：
 * 1. 将链表转换为流，去除重复的节点。
 * 2. 将结果转换回链表。
 */

import java.util.HashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.stream.Collectors;

class ListNode {
    int val;
    ListNode next;
    ListNode(int x) { val = x; }
}

public class Solution {
    public ListNode removeDuplicateNodes(ListNode head) {
        if (head == null) return head;
        List<Integer> values = new LinkedList<>();
        ListNode current = head;
        while (current != null) {
            values.add(current.val);
            current = current.next;
        }
        List<Integer> distinctValues = values.stream().distinct().collect(Collectors.toList());
        ListNode dummy = new ListNode(0);
        ListNode newCurrent = dummy;
        for (int value : distinctValues) {
            newCurrent.next = new ListNode(value);
            newCurrent = newCurrent.next;
        }
        return dummy.next;
    }
}