720. Longest Word in Dictionary

Easy

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.

If there is no answer, return the empty string.

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:

All the strings in the input will only contain lowercase letters.

The length of words will be in the range [1, 1000].

The length of words[i] will be in the range [1, 30].

1. always start from brute force:

   可以使用set来加速查找的时间。然后预先排好序（长度从大到小，字典顺序）找到的第一个符合条件的一定就是最优解

class Solution:
    def longestWord(self, words: List[str]) -> str:
        wordset = set(words) # speed up find process
        words = sorted(words, key = lambda c: (-len(c), c))
        
        for w in words:
            if all(w[:k] in wordset for k in range(1, len(w))):
                return w