Longest Common Prefix

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

Solution:
class Solution {
public:
    string longestCommonPrefix(vector<string> &strs) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int size = strs.size();       
        if (size == 0)
            return "";
        else if (size == 1)
            return strs[0];
        else if (size == 2) {
            return find_min(strs[0], strs[1]);
        } else {
            vector<string> first(strs.begin(), strs.begin() + size/2);
            vector<string> second(strs.begin() + size/2, strs.end());
            return find_min(longestCommonPrefix(first),
                longestCommonPrefix(second));
        }
    }
    string find_min(string first, string second) {
        string sol;
        int str_size = min(first.size(), second.size());
        for (int i = 0; i < str_size; i++) {
            if (first[i] == second[i])
                sol.push_back(first[i]);
            else
                break;
        }
        return sol;
    }
};