<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 lcp(string &s1,string &s2){
        int i,j,n=s1.length(),m=s2.length();
        i=0;j=0;
        while(i<n && j<m){
            if(s1[i] != s2[j]) break;
            i++;j++;
        }
        return s1.substr(0, min(i,j));
    }
    string get(vector<string> &v,int low,int high){
        if(low == high) return v[low];
        if(low > high) return "";
        int mid = (low+ high)/2;
        string s1,s2;
        s1 = get(v,low,mid);
        s2= get(v,mid+1,high);
        return lcp(s1,s2);
    }
    string longestCommonPrefix(vector<string>& v) {
        if(v.size() == 0) return "";
        return get(v,0,v.size() -1);
    }
};
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