<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>

class Solution final {
public:
    inline string reverseStr(string &str, const int k) const noexcept {
        const auto last{end(str)};
        auto iter{begin(str)};
        while (iter != last) {
            const auto nextIter{iter + min(last - iter, ptrdiff_t(k))};
            reverse(iter, nextIter);
            iter = nextIter + min(last - nextIter, ptrdiff_t(k));
        }
        return move(str);
    }
};

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