LeetCode: Linked List Cycle

双指针的简单题

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

 C#

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     public int val;
 *     public ListNode next;
 *     public ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public bool HasCycle(ListNode head) {
        if (head == null) return false;
        ListNode p = head, q = head;
        while (q != null) {
            q = q.next;
            if (q == null) break;
            if (p == q) return true;
            p = p.next;
            q = q.next;
        }
        return false;
    }
}