leetcode 524. Longest Word in Dictionary through Deleting

class Solution {
public:
    int max_len = 0;
    string result;
    // 对数组中的每个string都去判断是否可以由原string得到，过程中保存最长的字符串
    string findLongestWord(string s, vector<string>& d) {
        for(vector<string>::iterator p = d.begin(); p != d.end(); p++) {
            findMax(s, *p);
        }
        return result;
    }
    void findMax(string s, string dic) {
        int first;
        for(int i = 0; i < dic.length();i++) {
            first = s.find(dic[i]);
            if(first == -1) {
                return;
            }
            s.erase(0, first + 1);
        }
        if(max_len < dic.length()) {
            max_len = dic.length();
            result = dic;
        }
        else if(max_len == dic.length()) {
            if(result > dic)
                result = dic;
        }
    }
};