#leetcode #142 in cpp

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?

Solution: 

From http://bangbingsyb.blogspot.com/2014/11/leetcode-linked-list-cycle-i-ii.html

Code:

/**
* 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) {
ListNode *slow = head;
ListNode *fast = head;
int k = 0;
while(fast && fast->next){
fast = fast->next->next;
slow = slow->next;
k++;
if(slow == fast){
slow = head;
while(slow!=fast) {
fast = fast->next;
slow = slow->next;

}
return slow;
}
}
return NULL;
}
};