LeetCode 141. Linked List Cycle [Easy]

发表于 | 更新于 | 分类于 ， | 阅读次数：

LeetCode 141.

题目来源：https://leetcode.com/problems/linked-list-cycle

题目难度：Easy

1
2
3
4
5
6
7
8
9
10
11
12
13
// 链表的结构

/**
 * Definition for singly-linked list.
 * class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */

解法1[Java]：快慢指针

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
public class Solution {
    public boolean hasCycle(ListNode head) {
        if (head == null || head.next == null) {
            return false;
        }
        ListNode slow = head;
        ListNode fast = head.next;
        while (slow != fast) {
            if (fast == null || fast.next == null) {
                return false;
            }
            slow = slow.next;
            fast = fast.next.next;
        }
        return true;
    }
}

解法2[Java]：Hash表

1
2
3
4
5
6
7
8
9
10
11
12
public boolean hasCycle(ListNode head) {
    Set<ListNode> nodesSeen = new HashSet<>();
    while (head != null) {
        if (nodesSeen.contains(head)) {
            return true;
        } else {
            nodesSeen.add(head);
        }
        head = head.next;
    }
    return false;
}