Interchange the diagonal of a matrix in c++

C++ program for Interchange the diagonal of a matrix. Here more solutions.

// Include header file
#include <iostream>
#include <vector>
using namespace std;

//  stdc++ 11 program for
//  Swap diagonal elements of matrix using recursion
class Exchange {
    //  Method which are perform swap operation
    //  Here x and y indicate start and end rows
    //  p and q indicates start and end columns
    public :
    static void swapDiagonal(vector<vector<int>> &matrix, 
                             int x, 
                             int y, 
                             int p, 
                             int q)
    {
        if (x >= y || p >= q) {
            return;
        }
        int temp = matrix[x][p];
        //  Swap the element value
        matrix[x][p] = matrix[x][q];
        matrix[x][q] = temp;
        temp = matrix[y][p];
        //  Swap the element value
        matrix[y][p] = matrix[y][q];
        matrix[y][q] = temp;
        Exchange::swapDiagonal(matrix, x + 1, y - 1, p + 1, q - 1);
    }
    //  Display matrix elements
    static void showMatrix(vector<vector<int>> matrix, int size)
    {
        //  iterate rows
        for (int i = 0; i < size; ++i) {
            //  iterate columns
            for (int j = 0; j < size; ++j) {
                //  Display element value
                cout<<"  " << matrix[i][j];
            }
            //   include new line
            cout<<endl;
        }
        //  include new line
        cout<<endl;
    }
};
int main()
{
    //  Define matrix element
    vector<vector<int>> matrix {
      {1, 2, 3, 4},
      {5, 6, 7, 8},
      {9, 10, 11, 12},
      {13, 14, 15, 16}
    };
    //  Assume N X N matrix
    int n = matrix.size();
    //  Display element
    Exchange::showMatrix(matrix, n);
    //  interchange request
    Exchange::swapDiagonal(matrix, 0, n - 1, 0, n - 1);
    //  Display element
    Exchange::showMatrix(matrix, n);
}

Output

  1  2  3  4
  5  6  7  8
  9  10  11  12
  13  14  15  16

  4  2  3  1
  5  7  6  8
  9  11  10  12
  16  14  15  13