208. Implement Trie (Prefix Tree)

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

Example:

Trie trie = new Trie();

trie.insert("apple");
trie.search("apple");   // returns true
trie.search("app");     // returns false
trie.startsWith("app"); // returns true
trie.insert("app");   
trie.search("app");     // returns true

Note:

• You may assume that all inputs are consist of lowercase letters a-z.
• All inputs are guaranteed to be non-empty strings.

实现字典树

C++：

class Trie {
    
    private class Node{
        Node[] childs = new Node[26] ;
        boolean isLeaf ;
    }
    
    private Node root = new Node() ;

    /** Initialize your data structure here. */
    public Trie() {
        
    }
    
    /** Inserts a word into the trie. */
    public void insert(String word) {
        insert(word,root) ;
    }
    
    public void insert(String word , Node node) {
        if (node == null)
            return ;
        if (word.length() == 0){
            node.isLeaf = true ;
            return ;
        }
        int index = word.charAt(0) - 'a' ;
        if (node.childs[index] == null){
            node.childs[index] = new Node() ;
        }
        insert(word.substring(1) , node.childs[index]) ;
    }
    
    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        return search(word,root) ;
    }
    
    public boolean search(String word, Node node) {
        if (node == null)
            return false;
        if (word.length() == 0){
            return node.isLeaf ;
        }
        int index = word.charAt(0) - 'a' ;
        return search(word.substring(1) , node.childs[index]) ;
    }
    
    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
        return startsWith(prefix,root) ;
    }
    
    public boolean startsWith(String prefix , Node node) {
        if (node == null)
            return false;
        if (prefix.length() == 0){
            return true ;
        }
        int index = prefix.charAt(0) - 'a' ;
        return startsWith(prefix.substring(1) , node.childs[index]) ;
    }
}

/**
 * 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);
 */