1032.Stream-of-Characters

1032. Stream of Characters

题目地址

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);
*/