leetcode - Linked List Cycle II

 

/**
 * 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) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        ListNode * itr = head;
        ListNode * last = NULL;
        int n = 1;
        while (true){
            if (itr==NULL)
                return NULL;
            ListNode * tmp = itr;
            for (int i=0; i<n; i++){
                tmp = tmp->next;
                if (tmp==NULL)
                    return NULL;
                else if (tmp == itr){
                    ListNode * rlt = head;
                    while (true){
                        ListNode * rltItr = rlt;
                        for (int j=0; j<=i; j++){
                            rltItr = rltItr->next;
                            if (rltItr == rlt)
                                return rlt;
                        }
                        rlt = rlt->next;
                    }
                }
            }
            n++;
            itr = itr->next;
        }
        return NULL;
    }
};