leedcode 720 Longest Word in Dictionary java

博客围绕从英文词典中找可逐字符构建的最长单词展开。给定字符串列表代表英文词典,若有多个答案,返回字典序最小的最长单词;若无答案则返回空字符串,并给出两个示例说明解题场景。

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”.

import java.util.*;
class Solution {
    public String longestWord(String[] words) {
        String ans = "";//初始化一个字符串
        Set<String> wordset = new HashSet();//hashset不存储重复的字符串
        for (String word: words) wordset.add(word);把所有的字符串存进hashset
        for (String word: words) {
            if (word.length() > ans.length() ||
                    word.length() == ans.length() && word.compareTo(ans) < 0) {//如果长度打入ans或者相等于ans但是比ans靠后
                boolean good = true;//假设是真的
                for (int k = 1; k < word.length(); ++k) {
                    if (!wordset.contains(word.substring(0, k))) {//在hashset找到子串
                        good = false;
                        break;
                    }
                }
                if (good) ans = word;//如果真则ans=word
            }
        }
        return ans;
    }
}
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