Reverse String II
<p>Given a string <code>s</code> and an integer <code>k</code>, reverse the first <code>k</code> characters for every <code>2k</code> characters counting from the start of the string.</p>

<p>If there are fewer than <code>k</code> characters left, reverse all of them. If there are less than <code>2k</code> but greater than or equal to <code>k</code> characters, then reverse the first <code>k</code> characters and leave the other as original.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre><strong>Input:</strong> s = "abcdefg", k = 2
<strong>Output:</strong> "bacdfeg"
</pre><p><strong class="example">Example 2:</strong></p>
<pre><strong>Input:</strong> s = "abcd", k = 2
<strong>Output:</strong> "bacd"
</pre>
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= s.length &lt;= 10<sup>4</sup></code></li>
	<li><code>s</code> consists of only lowercase English letters.</li>
	<li><code>1 &lt;= k &lt;= 10<sup>4</sup></code></li>
</ul>
Two Pointers; String
function reverseStr(s: string, k: number): string {
    const n = s.length;
    const cs = s.split('');
    for (let i = 0; i < n; i += 2 * k) {
        for (let l = i, r = Math.min(i + k - 1, n - 1); l < r; l++, r--) {
            [cs[l], cs[r]] = [cs[r], cs[l]];
        }
    }
    return cs.join('');
}
