title

problem link

A zero-indexed array A of length N contains all integers from 0 to N-1. Find and return the longest length of set S, where S[i] = {A[i], A[A[i]], A[A[A[i]]], … } subjected to the rule below.

Suppose the first element in S starts with the selection of element A[i] of index = i, the next element in S should be A[A[i]], and then A[A[A[i]]]… By that analogy, we stop adding right before a duplicate element occurs in S.

Example 1:
Input: A = [5,4,0,3,1,6,2]
Output: 4
Explanation: 
A[0] = 5, A[1] = 4, A[2] = 0, A[3] = 3, A[4] = 1, A[5] = 6, A[6] = 2.

One of the longest S[K]:
S[0] = {A[0], A[5], A[6], A[2]} = {5, 6, 2, 0}

solution

使用-1标记已经看过的

class Solution {
public:
	int arrayNesting(vector<int>& nums) {
		int res = -1;
		for (int i = 0; i < nums.size(); i++) {
			if (nums[i] == -1)
				continue;
			int t = i,k=0;
			while (nums[t]>=0)
			{
				k++;
				int m = nums[t];
				nums[t] = -1;
				t = m;
			}
			res = max(res, k);
		}
		return res;
	}
};