ArrayNesting.cpp

//A zero-indexed array A consisting of N different integers is given. The array contains all integers in the range [0, N - 1].
//
//Sets S[K] for 0 <= K < N are defined as follows:
//
//S[K] = { A[K], A[A[K]], A[A[A[K]]], ... }.
//
//Sets S[K] are finite for each K and should NOT contain duplicates.
//
//Write a function that given an array A consisting of N integers, return the size of the largest set S[K] for this array.
//
//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}
//Note:
//N is an integer within the range [1, 20,000].
//The elements of A are all distinct.
//Each element of array A is an integer within the range [0, N-1].

#include<vector>

using namespace std;

class ArrayNesting {
public:
	int arrayNesting(vector<int>& nums) {
		int res = 0;
		vector<bool> vis(nums.size());
		for (size_t i = 0; i<nums.size(); ++i)
		{
			if (!vis[i])
			{
				int t = 0;
				while (!vis[i])
				{
					++t;
					vis[i] = true;
					i = nums[i];
				}
				if (t>res) res = t;
			}
		}
		return res;
	}
};