SquareMatrix.java

/*
Input 1:
[1,2,3,4]
[6,7,8,9]
[3,4,5,6]
[8,9,3,4]

Output 1:
[6,1,2,3]
[3,4,7,4]
[8,5,8,9]
[9,3,4,6]

Input 2:
[1,2,3,4,5]
[6,7,8,9,2]
[3,4,5,6,7]
[8,9,3,4,5]
[2,3,5,6,7]

Output 2:
[6,1,2,3,4]
[3,4,7,8,5]
[8,9,5,9,2]
[2,3,4,6,7]
[3,5,6,7,5]
 */
public class SquareMatrix {

    static int[][] even = {{1, 2, 3, 4}, {6, 7, 8, 9}, {3, 4, 5, 6}, {8, 9, 3, 4}};
    static int[][] evenResult = {{6, 1, 2, 3}, {3, 4, 7, 4}, {8, 5, 8, 9}, {9, 3, 4, 6}};
    static int[][] uneven = {{1, 2, 3, 4, 5}, {6, 7, 8, 9, 2}, {3, 4, 5, 6, 7}, {8, 9, 3, 4, 5}, {2, 3, 5, 6, 7}};
    static int[][] unevenResult = {{6, 1, 2, 3, 4}, {3, 4, 7, 8, 5}, {8, 9, 5, 9, 2}, {2, 3, 4, 6, 7}, {3, 5, 6, 7, 5}};

    public static void main(String[] args) {
        compare(resolve(even), evenResult);
        compare(resolve(uneven), unevenResult);
    }

    private static int[][] resolve(int[][] input) {
        boolean isUneven = (input.length % 2) != 0;
        int numberOfIterations = input.length / 4;
        int center = input.length / 2;
        int[][] result = new int[input.length][input.length];

        for (int i = 0; i <= numberOfIterations; i++) {
            result = rotate(result, input, i);
        }

        if (isUneven) {
            result[center][center] = input[center][center];
        }
        return result;
    }

    private static int[][] rotate(int[][] result, int[][] input, int row) {
        int nextRow = row + 1;
        int length = input.length;

        for (int i = row; i < length - nextRow; i++) {
            result[row][i + 1] = input[row][i];
        }

        for (int i = row; i < length - nextRow; i++) {
            result[i + 1][length - nextRow] = input[i][length - nextRow];
        }

        for (int i = length - nextRow; i > row; i--) {
            result[length - nextRow][i - 1] = input[length - nextRow][i];
        }

        for (int i = length - nextRow; i > row; i--) {
            result[i - 1][row] = input[i][row];
        }

        return result;
    }

    private static boolean compare(int[][] result, int[][] expected) {
        for (int i = 0; i < result.length; i++) {
            for (int j = 0; j < result.length; j++) {
                if (result[i][j] != expected[i][j]) {
                    throw new Error();
                }
            }
        }
        return true;
    }
}