[刷题]Linked List Cycle II

最新推荐文章于 2022-04-25 10:26:53 发布

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本文详细介绍了如何使用双指针法检测链表中的循环，并通过具体实例展示了算法实现过程，包括代码解析与运行结果分析。

[LintCode]Linked List Cycle II

/**
 * Definition for ListNode.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int val) {
 *         this.val = val;
 *         this.next = null;
 *     }
 * }
 */ 
public class Solution {
    /**
     * @param head: The first node of linked list.
     * @return: The node where the cycle begins. 
     *           if there is no cycle, return null
     */
    public ListNode detectCycle(ListNode head) {  
        // 2015-5-31 实在想不到
        if (head == null || head.next==null) {
            return null;
        }

        ListNode fast, slow;
        fast = head.next;
        slow = head;
        while (fast != slow) {
            if(fast==null || fast.next==null)
                return null;
            fast = fast.next.next;
            slow = slow.next;
        } 
        
        while (head != slow.next) {
            head = head.next;
            slow = slow.next;
        }
        return head;
    }
}