[LeetCode] Linked List Cycle II

null

class Solution {
public:
ListNode *detectCycle(ListNode *head) {
ListNode *p = head;
ListNode *q = head;
while(q && q -> next){
p = p -> next;
q = q -> next ->next;
if(p == q)
break;
}
if(q == NULL || q -> next == NULL)
return NULL;
p = head;
while(p != q){
p = p -> next;
q = q -> next;
}
return p;
}
};