README.md

2D Spiral Array

Find the pattern and complete the function: int[][] spiral(int n) where n is the size of the 2D array.

Sample Result

input = 3
123
894
765

input = 4
01 02 03 04
12 13 14 05
11 16 15 06
10 09 08 07

input = 8
1 2 3 4 5 6 7 8
28 29 30 31 32 33 34 9
27 48 49 50 51 52 35 10
26 47 60 61 62 53 36 11
25 46 59 64 63 54 37 12
24 45 58 57 56 55 38 13
23 44 43 42 41 40 39 14
22 21 20 19 18 17 16 15

spiral.py

from itertools import cycle

def spiral(n):
    grid = [[0 for x in range(n)] for y in range(n)]

    directions = cycle([
        lambda x,y: [x+1, y],
        lambda x,y: [x, y+1],
        lambda x,y: [x-1, y],
        lambda x,y: [x, y-1]
    ])
    
    current_direction = next(directions)
    current_cord = [0, 0]
    for num in range(0, n * n):
        x, y = current_cord
        grid[y][x] = num+1

        cx, cy = current_direction(x, y)
        if cx < 0 or cx >= n or cy < 0 or cy >= n or grid[cy][cx] != 0:
            current_direction = next(directions)

        current_cord = current_direction(x, y)

    return grid

import unittest
class TestSpiralMethods(unittest.TestCase):
    def test_one(self):
        self.assertEqual(spiral(1), [[1]])

    def test_two(self):
        self.assertEqual(spiral(2), [
            [1, 2], 
            [4, 3]])

    def test_three(self):
        self.assertEqual(spiral(3), [
            [1, 2, 3], 
            [8, 9, 4],
            [7, 6, 5]])

unittest.main(exit=False)