Leetcode Longest Common Prefix

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

class Solution {
public:
    string longestCommonPrefix(vector<string> &strs) {
        if(strs.empty()) return "";
        int minLength = strs[0].length();
        for(int i = 0 ; i < strs.size(); ++ i) minLength = min(minLength,(int)strs[i].length());
        bool flag = false;
        int i = 0;
        for(i = 0 ; i < minLength; ++ i){
            char ch = strs[0][i];
            for(int j = 1; j < strs.size(); ++ j){
                if(strs[j][i]!=ch){flag=true;break;}
            }
            if(flag) break;
        }
        return strs[0].substr(0,i);
    }
};