1032. Stream of Characters.md

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.

class TrieNode{
    TrieNode[] children;
    boolean isWord;
    public TrieNode(){
        children=new TrieNode[26];
        isWord=false;
    }
}
class StreamChecker {
    TrieNode root;
    StringBuilder stream;
    public StreamChecker(String[] words) {
        root=new TrieNode();
        builtTrie(root,words);
        stream=new StringBuilder();
    }
    
    public boolean query(char letter) {
        stream.append(letter);
        TrieNode curr=root;
        for(int i=stream.length()-1;i>=0;i--){
            if(curr.children[stream.charAt(i)-'a']==null){
                return false;
            }
            curr=curr.children[stream.charAt(i)-'a'];
            if(curr.isWord) return true;
        }
        return false;
    }
    public void builtTrie(TrieNode root,String[] words){
        for(String s:words){
            TrieNode curr=root;
            StringBuilder sb=new StringBuilder(s);
            sb=sb.reverse();
            for(char ch:sb.toString().toCharArray()){
                if(curr.children[ch-'a']==null) curr.children[ch-'a']=new TrieNode();
                curr=curr.children[ch-'a'];
            }
            curr.isWord=true;
        }
    }
}

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