LeetCode题解：Linked List Cycle

/**
* 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) {
if(head==null) return false;
ListNode walker = head;
ListNode runner = head;
while(runner.next!=null && runner.next.next!=null) {
walker = walker.next;
runner = runner.next.next;
if(walker==runner) return true;
}
return false;
}
}

题意：判断链表是否有环

解题思路：快慢指针，若存在环，两指针必定相遇

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) {
        if(head==null) return false;
        ListNode walker = head;
        ListNode runner = head;
        while(runner.next!=null && runner.next.next!=null) {
            walker = walker.next;
            runner = runner.next.next;
            if(walker==runner) return true;
        }
        return false;
    }
}