原题链接在这里:https://leetcode.com/problems/replace-words/description/

题目:

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:

  1. The input will only have lower-case letters.
  2. 1 <= dict words number <= 1000
  3. 1 <= sentence words number <= 1000
  4. 1 <= root length <= 100
  5. 1 <= sentence words length <= 1000

题解:

利用Trie树. 把dict中每个词先放进Trie树中.

对于sentence按照空格拆分出的token, 从头添加token的char, 试验是否能在Trie树中找到. 找到说明加到这就是个root了, 可以返回.

若是Trie树中都没有starts with当前值时说明这个token 没有root, 返回原token.

Time Complexity: O(n*m + k*p). n = dict.size(). m是dict中单词平均长度. k是sentence中token个数. p是token平均长度.

Space: O(n*m+k).

AC Java:

 class Solution {
public String replaceWords(List<String> dict, String sentence) {
if(sentence == null || sentence.length() == 0 || dict == null || dict.size() == 0){
return sentence;
} Trie trie = new Trie();
for(String word : dict){
trie.insert(word);
} String [] tokens = sentence.split("\\s+"); StringBuilder sb = new StringBuilder();
for(String token : tokens){
sb.append(getRootOrDefault(token, trie) + " ");
} sb.deleteCharAt(sb.length()-1);
return sb.toString();
} private String getRootOrDefault(String s, Trie trie){
StringBuilder sb = new StringBuilder();
for(int i = 0; i<s.length(); i++){
sb.append(s.charAt(i));
if(trie.search(sb.toString())){
return sb.toString();
}else if(!trie.startsWith(sb.toString())){
return s;
}
}
return s;
}
} class Trie{
private TrieNode root; public Trie(){
root = new TrieNode();
} public void insert(String word){
TrieNode p = root;
for(char c : word.toCharArray()){
if(p.nexts[c-'a'] == null){
p.nexts[c-'a'] = new TrieNode();
}
p = p.nexts[c-'a'];
} p.val = word;
} public boolean search(String word){
TrieNode p = root;
for(char c : word.toCharArray()){
if(p.nexts[c-'a'] == null){
return false;
}
p = p.nexts[c-'a'];
}
return p.val.equals(word);
} public boolean startsWith(String word){
TrieNode p = root;
for(char c : word.toCharArray()){
if(p.nexts[c-'a'] == null){
return false;
}
p = p.nexts[c-'a'];
}
return true;
}
} class TrieNode{
String val = "";
TrieNode [] nexts; public TrieNode(){
nexts = new TrieNode[26];
}
}

Another implementation.

 class Solution {
public String replaceWords(List<String> dict, String sentence) {
if(sentence == null || sentence.length() == 0 || dict == null || dict.size() == 0){
return sentence;
} TrieNode root = new TrieNode();
for(String word : dict){
TrieNode p = root;
for(char c : word.toCharArray()){
if(p.nexts[c-'a'] == null){
p.nexts[c-'a'] = new TrieNode();
} p = p.nexts[c-'a'];
} p.val = word;
} String [] words = sentence.split("\\s+");
for(int i = 0; i<words.length; i++){
TrieNode p = root;
for(char c : words[i].toCharArray()){
if(p.nexts[c-'a'] == null || p.val != null){
break;
} p = p.nexts[c-'a'];
} words[i] = (p.val == null) ? words[i] : p.val;
} return String.join(" ", words);
}
} class TrieNode{
String val;
TrieNode [] nexts; public TrieNode(){
nexts = new TrieNode[26];
}
}

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