Maximum Swap
<p>You are given an integer <code>num</code>. You can swap two digits at most once to get the maximum valued number.</p>

<p>Return <em>the maximum valued number you can get</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> num = 2736
<strong>Output:</strong> 7236
<strong>Explanation:</strong> Swap the number 2 and the number 7.
</pre>

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

<pre>
<strong>Input:</strong> num = 9973
<strong>Output:</strong> 9973
<strong>Explanation:</strong> No swap.
</pre>

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

<ul>
	<li><code>0 &lt;= num &lt;= 10<sup>8</sup></code></li>
</ul>
Greedy; Math
function maximumSwap(num: number): number {
    const list = new Array();
    while (num !== 0) {
        list.push(num % 10);
        num = Math.floor(num / 10);
    }
    const n = list.length;
    const idx = new Array();
    for (let i = 0, j = 0; i < n; i++) {
        if (list[i] > list[j]) {
            j = i;
        }
        idx.push(j);
    }
    for (let i = n - 1; i >= 0; i--) {
        if (list[idx[i]] !== list[i]) {
            [list[idx[i]], list[i]] = [list[i], list[idx[i]]];
            break;
        }
    }
    let res = 0;
    for (let i = n - 1; i >= 0; i--) {
        res = res * 10 + list[i];
    }
    return res;
}
