leetcode-14 Longest Common Prefix

class Solution {
public:
    string longestCommonPrefix(vector<string> &strs) {
        string res;
        int len = strs.size();
        if(len == 0) return res; //这句一定得有，如果不加的话，第一个for循环运行到strs[0].size()，就会出现runtime error，因为根本就没有strs[0]
        int i,j;
        for(i = 0; i < strs[0].size(); i++){
            for(j = 1; j < len; j++){
                if(strs[j].size() == i || strs[j][i] != strs[0][i])
                    return res;
            }
            res.push_back(strs[0][i]);
        }
        return res;
    }
};