Leetcode 142. Linked List Cycle II

文章作者：Tyan
博客：noahsnail.com  |  CSDN  | 

1. Description

Linked List Cycle II

2. Solution

/**
 * 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) {
        if(!head) {
            return nullptr;
        }
        ListNode* slow = head;
        ListNode* fast = head;
        while(true) {
            if(fast == nullptr || fast->next == nullptr) {
                return nullptr;
            }
            slow = slow->next;
            fast = fast->next->next;
            if(slow == fast) {
                break;
            }
        }
        slow = head;
        while(slow != fast) {
            slow = slow->next;
            fast = fast->next;
        }
        return slow;
    }
};

Reference

1. https://leetcode.com/problems/linked-list-cycle-ii/description/