[leetcode] Implement Trie (Prefix Tree)

没什么好说的。code非常直观

class TrieNode {
    // Initialize your data structure here.
    HashMap children = new HashMap();
    boolean isWord = false;
    char currentChar;

    public TrieNode() {
        
    }

    public TrieNode(char in){
        currentChar = in;
    }

    public void addChild(char kid){
        if (children.containsKey(kid)){
            return;
        }
        children.put(kid, new TrieNode(kid));
    }


    public boolean hasChild(char kid){
        return children.containsKey(kid);
    }

    public TrieNode getChild(char kid){
        if (!hasChild(kid)){
            return null;
        }
        return children.get(kid);
    }

    public boolean isNodeWordEnd(){
        return isWord;
    }
    
    public void setNodeAWordEnd(){
        isWord = true;
    }
}

public class Trie {
    private TrieNode root;

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

    // Inserts a word into the trie.
    public void insert(String word) {
        TrieNode node = root;
        for (int i = 0; i < word.length(); i++){
            char temp = word.charAt(i);
            if (!node.hasChild(temp)){
                node.addChild(temp);
            }
            node = node.getChild(temp);
        }
        node.setNodeAWordEnd();
    }

    // Returns if the word is in the trie.
    public boolean search(String word) {
        TrieNode node = root;
        for (int i = 0; i < word.length(); i++){
            char temp = word.charAt(i);
            if (!node.hasChild(temp)){
                return false;
            }
            node = node.getChild(temp);
        }
        return node.isNodeWordEnd();
    }

    // Returns if there is any word in the trie
    // that starts with the given prefix.
    public boolean startsWith(String prefix) {
        TrieNode node = root;
        for (int i = 0; i < prefix.length(); i++){
            char temp = prefix.charAt(i);
            if (!node.hasChild(temp)){
                return false;
            }
            node = node.getChild(temp);
        }
        return true;
    }
}

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