Leetcode 648.单词替换

单词替换

在英语中，我们有一个叫做 词根(root)的概念，它可以跟着其他一些词组成另一个较长的单词——我们称这个词为 继承词(successor)。例如，词根an，跟随着单词 other(其他)，可以形成新的单词 another(另一个)。

现在，给定一个由许多词根组成的词典和一个句子。你需要将句子中的所有继承词用词根替换掉。如果继承词有许多可以形成它的词根，则用最短的词根替换它。

你需要输出替换之后的句子。

示例 1:

输入: dict(词典) = ["cat", "bat", "rat"]

sentence(句子) = "the cattle was rattled by the battery"

输出: "the cat was rat by the bat"

注:

1. 输入只包含小写字母。
2. 1 <= 字典单词数 <=1000
3. 1 <=  句中词语数 <= 1000
4. 1 <= 词根长度 <= 100
5. 1 <= 句中词语长度 <= 1000

思路

Intuition

For each word in the sentence, we'll look at successive prefixes and see if we saw them before.

Algorithm

Store all the roots in a Set structure. Then for each word, look at successive prefixes of that word. If you find a prefix that is a root, replace the word with that prefix. Otherwise, the prefix will just be the word itself, and we should add that to the final sentence answer.

public String[] split(String regex)根据给定的正则表达式的匹配来拆分此字符串。

然后就要明确正则表达式的含义了：

\s表示 空格,回车,换行等空白符,

+号表示一个或多个的意思

import java.util.HashSet;
import java.util.List;
import java.util.Set;

class Solution {
public String replaceWords(List<String> roots, String sentence) {
Set<String> rootset = new HashSet();
for (String root: roots) rootset.add(root);

StringBuilder ans = new StringBuilder();
for (String word: sentence.split("\s+")) {
String prefix = "";
for (int i = 1; i <= word.length(); ++i) {
prefix = word.substring(0, i);
if (rootset.contains(prefix)) break;
}
if (ans.length() > 0) ans.append(" ");
ans.append(prefix);
}
return ans.toString();
}
}