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

If there is no common prefix, return an empty string "".

Example 1:

Input: ["flower","flow","flight"]
Output: "fl"

Example 2:

Input: ["dog","racecar","car"]
Output: ""
Explanation: There is no common prefix among the input strings.

Note:

All given inputs are in lowercase letters a-z.

力扣惯例，传空参数进来。。。。

class Solution {
public:
    string longestCommonPrefix(vector<string>& strs) {
        if(strs.size()==0){
            return "";
        }
        int max=0;
        char m=strs[0][0];
        int flag=1;
        while(flag){
          for(int i=0;i<strs.size();i++){
              
            if(strs[i].length()<=max||strs[i][max]!=strs[0][max]){
                flag=0;
            }
            }if(flag)max++;   
        }
        string ss=strs[0].substr(0,max);
        return ss;
        
    }
};