 A permutation A[0], A[1], ..., A[N1] is a sequence containing each integer between 0 and N1, inclusive, exactly once. Each permutation A of length N has a corresponding child array B of the same length, where B is defined as follows:
 B[0] = 0
 B[i] = A[B[i1]], for every i between 1 and N1, inclusive.
A permutation is considered perfect if its child array is also a permutation.
Below are given all permutations for N=3 with their child arrays. Note that for two of these permutations ({1, 2, 0} and {2, 0, 1}) the child array is also a permutation, so these two permutations are perfect.
Permutation Child array
{0, 1, 2} {0, 0, 0}
{0, 2, 1} {0, 0, 0}
{1, 0, 2} {0, 1, 0}
{1, 2, 0} {0, 1, 2}
{2, 0, 1} {0, 2, 1}
{2, 1, 0} {0, 2, 0}
You are given a int[] P containing a permutation of length N. Find a perfect permutation Q of the same length such that the difference between P and Q is as small as possible, and return this difference. The difference between P and Q is the number of indices i for which P[i] and Q[i] are different. 
 {4, 2, 6, 0, 3, 5, 9, 7, 8, 1} 
 Returns: 5  
