LeetCode/LeetCode-142.cpp at master · hello-sources/LeetCode · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */
struct ListNode *detectCycle(struct ListNode *head) {
    struct ListNode *p = head, *q = head;
    if (p == NULL) return NULL;
    do {
        p = p->next;
        q = q->next;
        if (q == NULL || q->next == NULL) return NULL;
        q = q->next;
    } while (p != q);
    int cnt = 0;
    do {
        cnt++;
        p = p->next;
    } while (p != q);
    p = head, q = head;
    while (cnt--) q = q->next;
    while (p != q) p = p->next, q = q->next;
    return p;
}