SnailSort.java

package main.java.kyu4;

/**
 * 4 kyu - Snail Sort
 *
 * https://www.codewars.com/kata/521c2db8ddc89b9b7a0000c1/
 *
 * Details:
 *
 * Given an n x n array, return the array elements arranged from outermost elements to the middle
 * element, traveling clockwise.
 */

import org.junit.Assert;
import org.junit.Test;

import java.util.Arrays;
import static java.util.stream.Collectors.joining;

public class SnailSort {
    public static int[] snail(int[][] array) {
        if (array == null || array.length == 0 || array.length == 1 && array[0].length == 0) {
            return new int[0];
        }

        final int height = array.length;
        final int width = array[0].length;
        final int lastY = height / 2;
        final int lastX = width % 2 == 0 ? width / 2 - 1 : width / 2;

        int y = 0, x = 0, dirX = 1, dirY = 0, i = 0;
        int leftBorder = -1, rightBorder = width;
        int upperBorder = -1, lowerBorder = height;
        int[] output = new int[height * width];

        while (true) {
            if (x == rightBorder && y == upperBorder + 1) {
                x--;
                y++;
                dirX = 0;
                dirY = 1;
                upperBorder++;
            } else if (x == leftBorder && y == lowerBorder - 1) {
                x++;
                y--;
                dirX = 0;
                dirY = -1;
                lowerBorder--;
            } else if (y == lowerBorder && x == rightBorder - 1) {
                y--;
                x--;
                dirX = -1;
                dirY = 0;
                rightBorder--;
            } else if (y == upperBorder && x == leftBorder + 1) {
                y++;
                x++;
                dirX = 1;
                dirY = 0;
                leftBorder++;
            }
            output[i] = array[y][x];

            if (y == lastY && x == lastX) {
                break;
            }

            x += dirX;
            y += dirY;
            i++;
        }

        return output;
    }

    @Test
    public void SnailTest1() {
        int[][] array
                = {{1, 2, 3},
                {4, 5, 6},
                {7, 8, 9}};
        int[] r = {1, 2, 3, 6, 9, 8, 7, 4, 5};
        test(array, r);
    }

    public String int2dToString(int[][] a) {
        return Arrays.stream(a).map(row -> Arrays.toString(row)).collect(joining("\n"));
    }

    public void test(int[][] array, int[] result) {
        String text = int2dToString(array) + " should be sorted to " + Arrays.toString(result);
        System.out.println(text);
        Assert.assertArrayEquals( result, snail(array));
    }

}