Longest Common Prefix

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

 1 class Solution {
 2 public:
 3     string longestCommonPrefix(vector<string> &strs) {
 4         string res;
 5         if(strs.empty()) 
 6             return res;
 7         for(int i = 0; i < strs[0].size(); i++) {
 8             char ch = strs[0][i];
 9             for(int j = 1; j < strs.size(); j++) {
10                 if(strs[j][i] != ch || i == strs[j].size()) {
11                     return res;
12                 }
13             }
14             res.push_back(ch);
15         }
16     }
17 };