leetcode 14

求公共前缀，两两比较即可

string the_common_prefix(const string &str1,const string &str2)
{
    string str="";
    for(int i=0,j=0;i<str1.size()&&j<str2.size();i++,j++)
    {
    if(str1[i]==str2[j]) 
    str.push_back(str1[i]);
    else break;
    }
    return str;
}
class Solution {
public:
    string longestCommonPrefix(vector<string>& strs) {
        if(strs.size()==0)return "";
        string The_Str=strs[0];
        for(int i=1;i<strs.size();i++)
            The_Str=the_common_prefix(The_Str,strs[i]);
            return The_Str;
    }
};