81 lines
2.6 KiB
Markdown
81 lines
2.6 KiB
Markdown
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---
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id: 5a23c84252665b21eecc801c
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title: Spiral matrix
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challengeType: 5
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---
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## Description
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<section id='description'>
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Produce a spiral array.
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A <i>spiral array</i> 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.
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For example, given <b>5</b>, produce this array:
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<pre>
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0 1 2 3 4
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15 16 17 18 5
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14 23 24 19 6
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13 22 21 20 7
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12 11 10 9 8
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</pre>
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</section>
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## Instructions
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<section id='instructions'>
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</section>
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## Tests
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<section id='tests'>
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``` yml
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tests:
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- text: <code>spiralArray</code> should be a function.
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testString: assert(typeof spiralArray=='function','<code>spiralArray</code> should be a function.');
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- text: <code>spiralArray(3)</code> should return a array.
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testString: assert(Array.isArray(spiralArray(3)), '<code>spiralArray(3)</code> should return a array.');
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- text: <code>spiralArray(3)</code> should return <code>[[0, 1, 2],[7, 8, 3],[6, 5, 4]]</code>.
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testString: assert.deepEqual(spiralArray(3), [[0, 1, 2], [7, 8, 3], [6, 5, 4]], '<code>spiralArray(3)</code> should return <code>[[0, 1, 2],[7, 8, 3],[6, 5, 4]]</code>.');
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- text: <code>spiralArray(4)</code> should return <code>[[0, 1, 2, 3],[11, 12, 13, 4],[10, 15, 14, 5],[9, 8, 7, 6]]</code>.
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testString: assert.deepEqual(spiralArray(4), [[0, 1, 2, 3], [11, 12, 13, 4], [10, 15, 14, 5], [9, 8, 7, 6]], '<code>spiralArray(4)</code> should return <code>[[0, 1, 2, 3],[11, 12, 13, 4],[10, 15, 14, 5],[9, 8, 7, 6]]</code>.');
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- text: <code>spiralArray(5)</code> should return <code>[[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]]</code>.
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testString: 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]], '<code>spiralArray(5)</code> should return <code>[[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]]</code>.');
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```
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</section>
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## Challenge Seed
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<section id='challengeSeed'>
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<div id='js-seed'>
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```js
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function spiralArray (n) {
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// Good luck!
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}
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```
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</div>
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</section>
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## Solution
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<section id='solution'>
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```js
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function spiralArray (n) {
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var arr = Array(n),
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x = 0, y = n,
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total = n * n--,
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dx = 1, dy = 0,
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i = 0, j = 0;
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while (y) arr[--y] = [];
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while (i < total) {
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arr[y][x] = i++;
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x += dx; y += dy;
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if (++j == n) {
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if (dy < 0) {x++; y++; n -= 2}
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j = dx; dx = -dy; dy = j; j = 0;
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}
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}
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return arr;
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}
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```
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</section>
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