curriculum/challenges/english/blocks/rosetta-code-challenges/5a23c84252665b21eecc801c.md
Produce a spiral array. A spiral array is a square arrangement of the first N<sup>2</sup> natural numbers, where the numbers increase sequentially as you go around the edges of the array spiraling inwards. For example, given 5, produce this array:
<pre> 0 1 2 3 4 15 16 17 18 5 14 23 24 19 6 13 22 21 20 7 12 11 10 9 8 </pre>spiralArray should be a function.
assert(typeof spiralArray == 'function');
spiralArray(3) should return an array.
assert(Array.isArray(spiralArray(3)));
spiralArray(3) should return [[0, 1, 2],[7, 8, 3],[6, 5, 4]].
assert.deepEqual(spiralArray(3), [
[0, 1, 2],
[7, 8, 3],
[6, 5, 4]
]);
spiralArray(4) should return [[0, 1, 2, 3],[11, 12, 13, 4],[10, 15, 14, 5],[9, 8, 7, 6]].
assert.deepEqual(spiralArray(4), [
[0, 1, 2, 3],
[11, 12, 13, 4],
[10, 15, 14, 5],
[9, 8, 7, 6]
]);
spiralArray(5) should return [[0, 1, 2, 3, 4],[15, 16, 17, 18, 5],[14, 23, 24, 19, 6],[13, 22, 21, 20, 7],[12, 11, 10, 9, 8]].
assert.deepEqual(spiralArray(5), [
[0, 1, 2, 3, 4],
[15, 16, 17, 18, 5],
[14, 23, 24, 19, 6],
[13, 22, 21, 20, 7],
[12, 11, 10, 9, 8]
]);
function spiralArray(n) {
}
function spiralArray(n) {
var arr = Array(n),
x = 0,
y = n,
total = n * n--,
dx = 1,
dy = 0,
i = 0,
j = 0;
while (y) arr[--y] = [];
while (i < total) {
arr[y][x] = i++;
x += dx;
y += dy;
if (++j == n) {
if (dy < 0) {
x++;
y++;
n -= 2;
}
j = dx;
dx = -dy;
dy = j;
j = 0;
}
}
return arr;
}