Write a function to find the longest common prefix string amongst an array of strings.
class Solution {
public:
string longestCommonPrefix(vector<string> &strs) {
const int m = strs.size();
string res;
if (m == 0) {
return res;
}
const int n = strs[0].size();
for (int i = 0; i < n; i++) {
for (int j = 1; j < m; j++) {
if (strs[0][i] != strs[j][i]) {
return res;
}
}
res += strs[0][i];
}
return res;
}
};