1032.Stream-of-Characters.md

1032. Stream of Characters

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题目地址

https://leetcode.com/problems/stream-of-characters/

题目描述

Implement the StreamChecker class as follows:

StreamChecker(words): Constructor, init the data structure with the given words.
query(letter): returns true if and only if for some k >= 1, the last k characters queried (in order from oldest to newest, including this letter just queried) spell one of the words in the given list.
 
Example:
StreamChecker streamChecker = new StreamChecker(["cd","f","kl"]); // init the dictionary.
streamChecker.query('a');          // return false
streamChecker.query('b');          // return false
streamChecker.query('c');          // return false
streamChecker.query('d');          // return true, because 'cd' is in the wordlist
streamChecker.query('e');          // return false
streamChecker.query('f');          // return true, because 'f' is in the wordlist
streamChecker.query('g');          // return false
streamChecker.query('h');          // return false
streamChecker.query('i');          // return false
streamChecker.query('j');          // return false
streamChecker.query('k');          // return false
streamChecker.query('l');          // return true, because 'kl' is in the wordlist
 
Note:
1 <= words.length <= 2000
1 <= words[i].length <= 2000
Words will only consist of lowercase English letters.
Queries will only consist of lowercase English letters.
The number of queries is at most 40000.

代码

Approach 1:

class StreamChecker {
  
  class TrieNode {
    boolean isWord;
    TrieNode[] next = new TrieNode[26];
  }
  
  TrieNode root = new TrieNode();
  StringBuilder sb = new StringBuilder();
  
  public StreamChecker(String[] words) {
		createTrie(words);
  }

  public boolean query(char letter) {
		sb.append(letter);
    TrieNode node = root;
    for (int i = sb.length() - 1; i >= 0 && node != null; i--) {
      char c = sb.charAt(i);
      node = node.next[c - 'a'];
      if (node != null && node.isWord) {
        return true;
      }
    }
    
    return false;
  }
  
  private void createTrie(String[] words) {
    for (String s : words) {
      TrieNode node = root;
      int len = s.length();
      for (int i = len - 1; i >= 0; i--) {
        char c = s.charAt(i);
        if (node.next[c - 'a'] == null) {
          node.next[c - 'a'] = new TrieNode();
        }
        node = node.next[c - 'a'];
      }
      node.isWord = true;
    }
  }
  
}

/**
 * Your StreamChecker object will be instantiated and called as such:
 * StreamChecker obj = new StreamChecker(words);
 * boolean param_1 = obj.query(letter);
 */