在原数组中修改的方法
先把矩形看作正方形，然后沿对角线对称一次，再左右对称一次

#include <iostream>
#include <cstring>
using namespace std;

const int N = 110;
int n, m, a[N][N], b[N][N];

int main()
{
    cin >> n >> m;
    for ( int i = 1; i <= n; i ++ )
        for ( int j = 1; j <= m; j ++ )
            cin >> a[i][j];
    for ( int i = 1; i <= max(n, m); i ++ )
        for ( int j = 1; j <= max(n, m); j ++ )
            b[i][j] = a[j][i];
    for ( int i = 1; i <= m; i ++ )
        for ( int j = 1; j <= n; j ++ )
            a[i][n + 1 - j] = b[i][j];
    for ( int i = 1; i <= m; i ++ )
    {
        for ( int j = 1; j <= n; j ++ )
            cout << a[i][j] << ' ';
        cout << endl;
    }
    return 0;
}