LeetCode-141~Linked List Cycle

Given a linked list, determine if it has a cycle in it.
Follow up:
Can you solve it without using extra space?
给定一个链表，检测内部是否有cycle

算法分析

方法一

通过哈希表来解决问题

Java代码

/**
 * Definition for singly-linked list.
 * class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public boolean hasCycle(ListNode head) {
        Set listSet = new HashSet<>();
        while(head != null) {
            if (listSet.contains(head))
                return true;
            else 
                listSet.add(head);
            head = head.next;
        }
        return false;
    }
}

参考

LeetCode