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

找出，給出的一堆字符串的公共前綴。兩個兩個比較

class Solution {
public:
    string getcom(string &a,string &b) {
        int m = min(a.size(), b.size());
        string t = "";
        for (int i = 0; i < m; ++i) {
            
 
if (a[i] != b[i]) return t; 
            else t += a[i];
        }
        return t;
    }
    string longestCommonPrefix(vector<string>& strs) {
        if (strs.size() == 0) return "";
        string s = strs[0];
        for (int i = 1; i < strs.size(); ++i) {
            s = getcom(s, strs[i]); 
        }
        
 
//cout<<s<<endl;
        return s;
    }
};

14. Longest Common Prefix