Linked List Cycle II

最新推荐文章于 2025-05-07 22:15:24 发布

最新推荐文章于 2025-05-07 22:15:24 发布 · 73 阅读

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本文介绍了一种高效算法来检测链表中是否存在循环，并找到循环开始的节点。通过两个指针快慢移动的方式，当两者相遇时，再从头结点与相遇点同步移动直至再次相遇即为循环起点。

Given a linked list, return the node where the cycle begins. If there is no cycle, return null.

/**
 * Definition for singly-linked list.
 * class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode detectCycle(ListNode head) {
    	if (head == null || head.next == null || head.next.next == null) {  
            return null;  
        }  
        ListNode n1 = head.next;  
        ListNode n2 = head.next.next;  
        while (n1 != n2) {  
            if (n2.next == null || n2.next.next == null) {  
                return null;  
            }  
            n1 = n1.next;  
            n2 = n2.next.next;  
        }  
        n2 = head;
        while (n1 != n2) {
        	n1 = n1.next;
        	n2 = n2.next;
        }
        return n1;  
    }
}