day-145.cpp

/*
  Stream of Characters


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.
*/

// Solved using trie, time complexity for insert & search: O(len(string))
// Created a class Trie, as characters will be always lower case so used array
// of 26 letters

class Trie {
    Trie* children[26];
    bool endOfWord;

   public:
    Trie() {
        endOfWord = false;
        for (int idx = 0; idx < 26; idx++) {
            children[idx] = NULL;
        }
    }

    void insert(string str) {
        Trie* trie = this;

        for (char ch : str) {
            if (trie->children[ch - 'a'] == NULL) {
                trie->children[ch - 'a'] = new Trie();
            }
            trie = trie->children[ch - 'a'];
        }

        trie->endOfWord = true;
    }

    bool search(deque<char>& stream) {
        Trie* trie = this;
        for (char ch : stream) {
            if (trie->children[ch - 'a'] == NULL) return false;
            trie = trie->children[ch - 'a'];
            if (trie->endOfWord) return true;
        }

        return false;
    }
};

class StreamChecker {
    Trie trie;
    deque<char> stream;

   public:
    StreamChecker(vector<string>& words) {
        for (string& word : words) {
            reverse(word.begin(), word.end());
            trie.insert(word);
        }
    }

    bool query(char letter) {
        stream.push_front(letter);
        return trie.search(stream);
    }
};