class Solution {
public:
string longestWord(vector<string>& words) {
sort(words.begin(), words.end()); //对字符串排好序，按照字符的ascll编码，匹配字典的排序
unordered_set<string> set;
string res = "";
for (int i = 0 ; i<words.size(); i++) {
if (words[i].size()==1||set.count(words[i].substr(0,words[i].size()-1))) {
res = words[i].size()>res.size() ? words[i]:res;
set.insert(words[i]);
}
}
return res;
}
};
