<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 lcp(strs, 0, strs.size()-1);
    }
    string CommonPrefixUtil(string str1, string str2){
        string result;
        int n1 = str1.length(), n2 = str2.length();

        for(int i=0,j=0; i<=n1-1 && j <= n2-1; i++,j++){
            if(str1[i] != str2[j]){
                break;
            }
            result.push_back(str1[i]);
        }
        return result;
    }

    string lcp(vector<string>& s, int low, int high){
        if(low == high){
            return s[low];
        }
        if(high > low){
            int mid = low + (high - low)/2;
            string str1 = lcp(s, low, mid);
            string str2 =  lcp(s, mid+1, high);

            return CommonPrefixUtil(str1, str2);
        }
        else{
            return s[low];
        }
    }
};
15500