<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 {
    string merge(string s1, string s2){
        if(s1=="") return "";
        if(s2=="") return "";
        string s = "";
        for(int i = 0; i<min(s1.size(), s2.size()); i++){
            if(s1[i]==s2[i]) s+=s1[i];
            else break;
        }
        return s;
    }
    string lcp(vector<string>& strs, int i, int j){
        if(i>j) return "";
        if(i==j) return strs[i];
        int mid = i + (j-i)/2;
        string s1 = lcp(strs, i, mid);
        string s2 = lcp(strs, mid+1, j);
        return merge(s1, s2);
    }
public:
    string longestCommonPrefix(vector<string>& strs) {
        return lcp(strs, 0, strs.size()-1);

        
    }
};
15700