01. Array Nesting.cpp

/*
Array Nesting
=============

You are given an integer array nums of length n where nums is a permutation of the numbers in the range [0, n - 1].

You should build a set s[k] = {nums[k], nums[nums[k]], nums[nums[nums[k]]], ... } subjected to the following rule:

The first element in s[k] starts with the selection of the element nums[k] of index = k.
The next element in s[k] should be nums[nums[k]], and then nums[nums[nums[k]]], and so on.
We stop adding right before a duplicate element occurs in s[k].
Return the longest length of a set s[k].

Example 1:
Input: nums = [5,4,0,3,1,6,2]
Output: 4
Explanation: 
nums[0] = 5, nums[1] = 4, nums[2] = 0, nums[3] = 3, nums[4] = 1, nums[5] = 6, nums[6] = 2.
One of the longest sets s[k]:
s[0] = {nums[0], nums[5], nums[6], nums[2]} = {5, 6, 2, 0}

Example 2:
Input: nums = [0,1,2]
Output: 1

Constraints:
1 <= nums.length <= 105
0 <= nums[i] < nums.length
All the values of nums are unique.
*/

class Solution {
public:
    int arrayNesting(vector<int>& A) {
        int ans = 0, n = A.size();
        vector<int> vis (n, 0);
        
        for(int i = 0; i < n; ++i) {
        
            if(vis[i] == 0) {
                int curr = i, count = 0;
                
                while(vis[curr] == 0) {
                    vis[curr] = 1;
                    count++;
                    curr = A[curr];
                }
                
                ans = max(ans, count);
            }
            
        }
        
        return ans;
    }
};