Leetcode Linked List Cycle II

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?

代码如下：

/**
* 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)
return NULL;

ListNode* one = head;
ListNode* two = head;
bool isCycle = false;
while(two->next && two->next->next)
{
one = one->next;
two = two->next->next;
if(one == two)
{
isCycle = true;
break;
}
}

if(isCycle == false)
return NULL;

one = head;
while(one != two)
{
one = one->next;
two = two->next;
}
return one;
}
};