Inplace rotate square matrix by 90 degrees by forming cycles

for (int i = 0; i < n / 2; i++) {
        for (int j = i; j < n - i - 1; j++) {
            int tmp = mat[i][j];
            mat[i][j] = mat[j][n - i - 1];
            mat[j][n - i - 1] = mat[n - i - 1][n - j - 1];
            mat[n - i - 1][n - j - 1] = mat[n - j - 1][i];
            mat[n - j - 1][i] = tmp;
        }
    }