# Create an n x n square matrix, where all the sub-matrix have the sum of opposite corner elements as even in Python // C++ program for// the above approach#include <bits/stdc++.h>using namespace std;void sub_mat_even(int N){  // Counter to initialize  // the values in 2-D array  int K = 1;     // To create a 2-D array  // from to 1 to N*2  int A[N][N];     for(int i = 0; i < N; i++)  {    for(int j = 0; j < N; j++)    {      A[i][j] = K;      K++;    }  }  // If found even we reverse  // the alternate row elements  // to get all diagonal elements  // as all even or all odd  if(N % 2 == 0)  {    for(int i = 0; i < N; i++)    {      if(i % 2 == 1)      {        int s = 0;        int l = N - 1;                 // Reverse the row        while(s < l)        {          swap(A[i][s],               A[i][l]);          s++;          l--;        }      }    }  }  // Print the formed array  for(int i = 0; i < N; i++)  {    for(int j = 0; j < N; j++)    {      cout << A[i][j] << " ";    }    cout << endl;  }}// Driver codeint main(){    int N = 4;       // Function call    sub_mat_even(N);}// This code is contributed by mishrapriyanshu557