[LeetCode] 208. Implement Trie (Prefix Tree)

Posted 2020-09-30

https://leetcode.com/problems/implement-trie-prefix-tree/#/description

Implement a trie with insert, search, and startsWith methods.

Note:
You may assume that all inputs are consist of lowercase letters a-z.

 

public class Trie {
    
    class TrieNode {
        private Map<Character, TrieNode> children;
        private boolean endOfWord;
        public TrieNode() {
            this.endOfWord = false;
            this.children = new HashMap<>();
        }
        public Map<Character, TrieNode> getChildren() {
            return this.children;
        }
        public boolean getEndOfWord() {
            return this.endOfWord;
        }
        public void setEndOfWord(boolean endOfWord) {
            this.endOfWord = endOfWord;
        }
    }

    private TrieNode trieTree = null;
    /** Initialize your data structure here. */
    public Trie() {
        this.trieTree = new TrieNode();
    }
    
    /** Inserts a word into the trie. */
    public void insert(String word) {
        TrieNode current = trieTree;
        for (int i = 0; i < word.length(); i++) {
            if (current.getChildren().containsKey(word.charAt(i))) {
                current = current.getChildren().get(word.charAt(i));
            } else {
                TrieNode newNode = new TrieNode();
                current.getChildren().put(word.charAt(i), newNode);
                current = newNode;
            }

            if (i == word.length() - 1) {
                current.setEndOfWord(true);
            }
        }
    }
    
    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        TrieNode current = trieTree;
        for (int i = 0; i < word.length(); i++) {
            if (!current.getChildren().containsKey(word.charAt(i))) {
                return false;
            }
            current = current.getChildren().get(word.charAt(i));
        }
        return current.getEndOfWord();
    }
    
    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
        TrieNode current = trieTree;
        for (int i = 0; i < prefix.length(); i++) {
            if (!current.getChildren().containsKey(prefix.charAt(i))) {
                return false;
            }
            current = current.getChildren().get(prefix.charAt(i));
        }
        return true;
    }
}

/**
 * Your Trie object will be instantiated and called as such:
 * Trie obj = new Trie();
 * obj.insert(word);
 * boolean param_2 = obj.search(word);
 * boolean param_3 = obj.startsWith(prefix);
 */