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720. Longest Word in Dictionary

题目

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].

题目大意

给出一个字符串数组 words 组成的一本英语词典。从中找出最长的一个单词，该单词是由 words 词典中其他单词逐步添加一个字母组成。若其中有多个可行的答案，则返回答案中字典序最小的单词。若无答案，则返回空字符串。

解题思路

• 给出一个字符串数组，要求找到长度最长的，并且可以由字符串数组里面其他字符串拼接一个字符组成的字符串。如果存在多个这样的最长的字符串，则输出字典序较小的那个字符串，如果找不到这样的字符串，输出空字符串。
• 这道题解题思路是先排序，排序完成以后就是字典序从小到大了。之后再用 map 辅助记录即可。