#链表 #环形链表 II

linked-list-cycle-ii.cpp

/**
 * 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 == NULL) return NULL;

        ListNode* slow = head;
        ListNode* fast = head;
        while (fast != NULL && fast->next != NULL) {
            slow = slow->next;
            fast = fast->next->next;

            if (slow == fast) {
                ListNode* tmp = head;
                while (tmp != fast) {
                    tmp = tmp->next;
                    fast = fast->next;
                }
                return tmp;
            }
        }
        return NULL;
    }
};