add: Stream of Characters

Author: sidvishnoi

1032-stream-of-characters.rs

@@ -0,0 +1,91 @@
+use std::cell::RefCell;
+use std::collections::VecDeque;
+
+#[derive(Default)]
+struct TrieNode {
+    is_word: bool,
+    children: [Option<Box<TrieNode>>; 26],
+}
+
+impl TrieNode {
+    fn new() -> Self {
+        Default::default()
+    }
+
+    fn insert(&mut self, word: Vec<u8>) {
+        let mut curr = self;
+        for ch in word.into_iter().map(|ch| (ch - b'a') as usize) {
+            let children = &mut curr.children[ch];
+            curr = children.get_or_insert_with(|| Box::new(TrieNode::new()))
+        }
+        curr.is_word = true;
+    }
+}
+
+struct StreamChecker {
+    trie: TrieNode,
+    last_queried: RefCell<VecDeque<u8>>,
+    max_word_length: usize,
+}
+
+impl StreamChecker {
+    fn new(words: Vec<String>) -> Self {
+        let max_word_length = words.iter().map(|word| word.len()).max().unwrap_or(0_usize);
+        let last_queried = VecDeque::with_capacity(max_word_length);
+
+        let mut trie = TrieNode::new();
+        for word in words {
+            let mut word = word.into_bytes();
+            word.reverse();
+            trie.insert(word);
+        }
+
+        Self {
+            trie,
+            last_queried: RefCell::new(last_queried),
+            max_word_length,
+        }
+    }
+
+    fn query(&self, letter: char) -> bool {
+        self.last_queried.borrow_mut().push_back(letter as u8);
+        if self.last_queried.borrow().len() > self.max_word_length {
+            self.last_queried.borrow_mut().pop_front();
+        }
+
+        let mut curr = &self.trie;
+        for &ch in self.last_queried.borrow().iter().rev() {
+            curr = match &curr.children[(ch - b'a') as usize] {
+                Some(trie) if trie.is_word => return true,
+                Some(trie) => trie,
+                None => break,
+            };
+        }
+        false
+    }
+}
+
+fn main() {
+    let sc = StreamChecker::new(vec!["cd".to_string(), "f".to_string(), "kl".to_string()]);
+    assert_eq!(false, sc.query('a'));
+    assert_eq!(false, sc.query('b'));
+    assert_eq!(false, sc.query('c'));
+    assert_eq!(true, sc.query('d'));
+    assert_eq!(false, sc.query('e'));
+    assert_eq!(true, sc.query('f'));
+    assert_eq!(false, sc.query('g'));
+    assert_eq!(false, sc.query('h'));
+    assert_eq!(false, sc.query('i'));
+    assert_eq!(false, sc.query('j'));
+    assert_eq!(false, sc.query('k'));
+    assert_eq!(true, sc.query('l'));
+
+    let sc = StreamChecker::new(vec!["abcde".to_string(), "ef".to_string()]);
+    assert_eq!(false, sc.query('a'));
+    assert_eq!(false, sc.query('b'));
+    assert_eq!(false, sc.query('c'));
+    assert_eq!(false, sc.query('d'));
+    assert_eq!(true, sc.query('e'));
+    assert_eq!(true, sc.query('f'));
+    assert_eq!(false, sc.query('g'));
+}