【LeetCode】Longest Common Prefix

class Solution {
public:
    string longestCommonPrefix(vector<string> &strs) {
        if(strs.empty())
            return "";    //这边要注意，string是类不是指针，所以不是NULL
        else if(strs.size() == 1)
            return strs[0];
        else
        {
            string ret = "";
            int num = 0;
            char c = strs[0][num];
            while(true)
            {
                for(vector<string>::size_type st = 0; st < strs.size(); st ++)
                {
                    if(num < strs[st].size() && strs[st][num] == c)
                    {//match
                        if(st == strs.size()-1)
                        {//end
                            ret += c;
                            num ++;
                            c = strs[0][num];
                            break;
                        }
                    }
                    else
                        return ret;
                }
            }
        }
    }
    
};