565. Array Nesting

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:

1. N is an integer within the range [1, 20,000].
2. The elements of A are all distinct.
3. Each element of array A is an integer within the range [0, N-1].

   class Solution {
   public:
       int arrayNesting(vector<int>& nums) {
               int len = nums.size();
           int N = len;
           int max = 0;
           int result = 0;
           for (int i = 0;i < len;i++)
           {
               if (nums[i] == N)
               {
                   continue;
               }
               else
               {
                   int k = i;
                   while (k < len&&nums[k] != N)
                   {
                       max++;
                       int k1 =nums[k];
                       nums[k] = N;
                       k = k1;
                   }
               }
               if (max > result)
               {
                   result = max;
               
               }
                   max = 0;
           }
           return result;
       }
   };