Square Matrix Rotation

matrix_rotation.groovy

def matrix = [[ 1, 2, 3, 4, 17],
              [ 5, 6, 7, 8, 18],
              [ 9,10,11,12, 19],
              [13,14,15,16, 20],
              [21,22,23,24, 25]]
/* Output
[21, 13, 9, 5, 1]
[22, 14, 10, 6, 2]
[23, 15, 11, 7, 3]
[24, 16, 12, 8, 4]
[25, 20, 19, 18, 17]
*/

def print2D(arr, n) {
    for (int i = 0 ; i < n ; i++){
        println arr.get(i)
    }
    println ""
}

def rotate(matrix, n) {
    for (int layer = 0 ; layer < n/2 ; layer++) { // 123
        int first = layer
        int last = n - layer - 1
        for (int i = first ; i <last; i++) {
            int offset = i-first
            // save top
            int top = matrix[first][i] // 1 2
            // bottom -> top
            matrix[first][i] = matrix[last-offset][first] // 1 -> 13 2 -> 9
            // bottom right -> bottom left
            matrix[last-offset][first] = matrix[last][last-offset] // 13 -> 16 9 -> 15
            // top left -> bottom left
            matrix[last][last-offset] = matrix[i][last] //  16 -> 4 8 -> 15
            // top left -> top right
            matrix[i][last] = top // 4 -> 1 
            print2D(matrix, n)
        }
        println "Next layer"
    }
} 

rotate(matrix, 5)