<p>Write a function to find the longest common prefix string amongst an array of strings.</p>

<p>If there is no common prefix, return an empty string <code>&quot;&quot;</code>.</p>

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

<pre>
<strong>Input:</strong> strs = [&quot;flower&quot;,&quot;flow&quot;,&quot;flight&quot;]
<strong>Output:</strong> &quot;fl&quot;
</pre>

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

<pre>
<strong>Input:</strong> strs = [&quot;dog&quot;,&quot;racecar&quot;,&quot;car&quot;]
<strong>Output:</strong> &quot;&quot;
<strong>Explanation:</strong> There is no common prefix among the input strings.
</pre>

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

<ul>
	<li><code>1 &lt;= strs.length &lt;= 200</code></li>
	<li><code>0 &lt;= strs[i].length &lt;= 200</code></li>
	<li><code>strs[i]</code> consists of only lowercase English letters.</li>
</ul>

class Solution {
public:
  string longestCommonPrefix(vector<string> &strs) {
    return aux(strs, 0, strs.size());
  }

private:
  string aux(vector<string> &strs, size_t begin, size_t end) {
    size_t n = end - begin;
    if (n == 1) {
      return strs[begin];
    } else if (n == 2) {
      size_t i;
      for (i = 0; i < min(strs[begin].size(), strs[end - 1].size()); ++i) {
        if (strs[begin][i] != strs[end - 1][i]) {
          return strs[begin].substr(0, i);
        }
      }
      if (i == strs[begin].size()) {
        return strs[begin];
      } else {
        return strs[end - 1];
      }
    } else {
      n /= 2;
      vector<string> tmp{aux(strs, begin, begin + n),
                         aux(strs, begin + n, end)};
      return aux(tmp, 0, 2);
    }
  }
};

13600