环形链表 II （ LeetCode 142 ）

https://leetcode.cn/problems/linked-list-cycle-ii/

请参考https://www.algomooc.com/746.html

public class Solution {
    public ListNode detectCycle(ListNode head) {
        ListNode slow=head;
        ListNode fast=head;

        while(fast!=null &&fast.next!=null)
        {
            slow=slow.next;
            fast=fast.next.next;

            if(slow==fast)
            {
                ListNode pointhead=head;
                ListNode pointcross=slow;

                while(pointhead!=pointcross)
                {
                    pointhead=pointhead.next;
                    pointcross=pointcross.next;
                }
                return pointcross;
            }
        }
        return null;
    }
}

class Solution {
public:
    ListNode *detectCycle(ListNode *head) {
        ListNode *slow=head;
        ListNode *fast=head;

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

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

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def detectCycle(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        slow=head
        fast=head
        while fast!=None and fast.next!=None:
            slow=slow.next
            fast=fast.next.next

            if slow==fast:
                pointhead=head
                pointcross=fast
                while pointhead!=pointcross:
                    pointhead=pointhead.next
                    pointcross=pointcross.next
                return pointcross
        return None