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648. Replace Words


In English, we have a concept called root, which can be followed by some other words to form another longer word - let’s call this word successor. For example, the root an, followed by other, which can form another word another.

Now, given a dictionary consisting of many roots and a sentence. You need to replace all the successor in the sentence with the root forming it. If a successor has many roots can form it, replace it with the root with the shortest length.

You need to output the sentence after the replacement.

Example 1:

Input: dict = ["cat", "bat", "rat"]
sentence = "the cattle was rattled by the battery"
Output: "the cat was rat by the bat"

Note:
The input will only have lower-case letters.
1 <= dict words number <= 1000
1 <= sentence words number <= 1000
1 <= root length <= 100
1 <= sentence words length <= 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.

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


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