Spiral Matrix II
<p>Given a positive integer <code>n</code>, generate an <code>n x n</code> <code>matrix</code> filled with elements from <code>1</code> to <code>n<sup>2</sup></code> in spiral order.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/0000-0099/0059.Spiral%20Matrix%20II/images/spiraln.jpg" style="width: 242px; height: 242px;" />
<pre>
<strong>Input:</strong> n = 3
<strong>Output:</strong> [[1,2,3],[8,9,4],[7,6,5]]
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> n = 1
<strong>Output:</strong> [[1]]
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= n &lt;= 20</code></li>
</ul>
Array; Matrix; Simulation
/**
 * @param {number} n
 * @return {number[][]}
 */
var generateMatrix = function (n) {
    const ans = Array.from({ length: n }, () => Array(n).fill(0));
    const dirs = [0, 1, 0, -1, 0];
    let [i, j, k] = [0, 0, 0];
    for (let v = 1; v <= n * n; v++) {
        ans[i][j] = v;
        const [x, y] = [i + dirs[k], j + dirs[k + 1]];
        if (x < 0 || x >= n || y < 0 || y >= n || ans[x][y] !== 0) {
            k = (k + 1) % 4;
        }
        i += dirs[k];
        j += dirs[k + 1];
    }
    return ans;
};
