[LeetCode]Linked List Cycle II

最新推荐文章于 2021-11-01 14:38:45 发布

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本文介绍了一种用于检测循环单链表的算法，包括定义了循环单链表结构，实现了一个检测循环的类及其私有方法，并通过实例展示了如何使用此类来查找循环节点。

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *detectCycle(ListNode *head) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        ListNode* fastWalker = head;
        if(hasCycle(head, fastWalker))
        {
            ListNode* cur = head;
            while(cur != fastWalker)
            {
                cur = cur->next;
                fastWalker = fastWalker->next;
            }
            return cur;
        }
        else return NULL;
    }
private:
    bool hasCycle(ListNode *head, ListNode*& fastWalker) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        ListNode* slowWalker = head;
        
        while(fastWalker && slowWalker)
        {
            fastWalker = fastWalker->next;
            if(fastWalker) fastWalker = fastWalker->next;
            else break;
            slowWalker = slowWalker->next;
            
            if(fastWalker == slowWalker) return true;
        }
        
        return false;
    }
};