LeetCode Replace Words

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];
     }
 }