Given a list of strings words representing an English Dictionary, find the longest word in words that can be built one character at a time by other words in words. If there is more than one possible answer, return the longest word with the smallest lexicographical order.

Example 1:

Input: 
words = ["w","wo","wor","worl", "world"]
Output: "world"
Explanation: 
The word "world" can be built one character at a time by "w", "wo", "wor", and "worl".

Example 2:

Input: 
words = ["a", "banana", "app", "appl", "ap", "apply", "apple"]
Output: "apple"
Explanation: 
Both "apply" and "apple" can be built from other words in the dictionary. However, "apple" is lexicographically smaller than "apply".

Note:

/**
 * @param {string[]} words
 * @return {string}
 */
var longestWord = function (words) {
    let res = "";
    words = words.sort();
    let 
 
set = new Set();
    for (let i in words) {
        let s = words[i];
        if (s.length == 1 || set.has(s.substring(0, s.length - 1))) {
            res = s.length > res.length ? s : res;
            set.add(s);
        }
    }
    return res;
};

720. Longest Word in Dictionary 字典中最長的單詞