208. Implement Trie (Prefix Tree)

/*
 * 208. Implement Trie (Prefix Tree) 
 * 2016-6-9 by Mingyang
 * 我在这里的时候用的hashmap来做的地图，这里用的是array，一样的原理
 * 不过我没有想到的是需要一个isEnd的property，因为这里的search必须找到end的时候才是成功的找到
 */
class Tries {
    public TrieNode root;
    public Tries() {
        root = new TrieNode();
        root.isEnd = true;
    }
    public void insert(String word) {
        if (word == null || word.length() == 0)
            return;
        TrieNode node = root;
        char[] letters = word.toCharArray();
        for (int i = 0; i < word.length(); i++) {
            int pos = letters[i] - ‘a‘;
            if (node.son[pos] == null) {
                node.son[pos] = new TrieNode();
                node.son[pos].val = letters[i];
            }
            node = node.son[pos];
        }
        node.isEnd = true;
    }
    // Returns if the word is in the trie.
    public boolean search(String word) {
        if (word == null || word.length() == 0) {
            return false;
        }
        TrieNode node = root;
        char[] letters = word.toCharArray();
        for (int i = 0; i < word.length(); i++) {
            int pos = letters[i] - ‘a‘;
            if (node.son[pos] != null) {
                node = node.son[pos];
            } else {
                return false;
            }
        }
        return node.isEnd;
    }
    // Returns if there is any word in the trie
    // that starts with the given prefix.
    public boolean startsWith(String prefix) {
        if (prefix == null || prefix.length() == 0) {
            return false;
        }
        TrieNode node = root;
        char[] letters = prefix.toCharArray();
        for (int i = 0; i < prefix.length(); i++) {
            int pos = letters[i] - ‘a‘;
            if (node.son[pos] != null) {
                node = node.son[pos];
            } else {
                return false;
            }
        }
        return true;
    }
}
class TrieNode {
    // Initialize your data structure here.
    TrieNode[] son;// 所有的儿子节点
    boolean isEnd;// 是不是最后一个节点
    char val;// 节点的值
    TrieNode() {
        this.son = new TrieNode[26];
        this.isEnd = false;
    }
}