题目描述(Medium)
Given a linked list, return the node where the cycle begins. If there is no cycle, return null.
Note: Do not modify the linked list.
Follow up:
Can you solve it without using extra space?
题目链接
https://leetcode.com/problems/linked-list-cycle-ii/description/
算法分析
详见之前的文章:【剑指】23.链表中环的入口结点
提交代码:
class Solution {
public:
ListNode *detectCycle(ListNode *head) {
if(!head || !head->next) return nullptr;
ListNode *slow = head, *fast = head;
while(slow && fast && fast->next)
{
slow = slow->next;
fast = fast->next->next;
if(slow == fast)
break;
}
// 如果没有环
if(!fast || !fast->next)
return nullptr;
fast = head;
while(slow != fast)
{
slow = slow->next;
fast = fast->next;
}
return slow;
}
};