208. Implement Trie (Prefix Tree)

Posted 2020-08-22 鱼与海洋

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

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

 

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class TrieNode {
    // Initialize your data structure here.
    HashMap<Character, TrieNode> map;
    boolean isWord;
    
    public TrieNode() {
        map = new HashMap<Character, TrieNode>();
        isWord = false;
    }
}

public class Trie {
    private TrieNode root;

    public Trie() {
        root = new TrieNode();
    }

    // Inserts a word into the trie.
    public void insert(String word) {
        TrieNode it = root;
        for(char c : word.toCharArray()){
            if(!it.map.containsKey(c)){
                it.map.put(c , new TrieNode() );
            }
            it = it.map.get(c);
        }
        it.isWord = true;
    }

    // Returns if the word is in the trie.
    public boolean search(String word) {
        TrieNode it = root;
        for(char c : word.toCharArray()){
            if(!it.map.containsKey(c)){
                return false;
            }
            it = it.map.get(c);
        }
        return it.isWord;
    }

    // Returns if there is any word in the trie
    // that starts with the given prefix.
    public boolean startsWith(String prefix) {
        TrieNode it = root;
        for(char c : prefix.toCharArray()){
            if(!it.map.containsKey(c)){
                return false;
            }
            it = it.map.get(c);
        }
        return true;
    }
}

// Your Trie object will be instantiated and called as such:
// Trie trie = new Trie();
// trie.insert("somestring");
// trie.search("key");