Topic:

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:

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

Example2:

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

Answer:

class Solution {
public:
    string longestCommonPrefix(vector<string>& strs) {
        if(strs.size()==0) return "";
        if(strs.size()==1) return strs[0];

        int minimum=strs[0].size();
        int growing_length=0;

        for(string s:strs){
            if(s.size()<minimum)
                minimum=s.size(); 
        }

        for(int j=0;j<minimum;j++){
            int judge=1;
            for(int i=1;i<strs.size();i++){
               if(strs[0].at(j)!=strs[i].at(j)){
                   judge=0;
               }   
            }
            if(judge==0&&j==0)
                return "";
            if(judge==1)
                growing_length++;

        }
        if(growing_length==0)
            return "";
        else
            return strs[0].substr(0,growing_length);


    }
};