Trie树的实现

Trie树也就是字典树，可以高效地用来进行字符串地检索。具体实现如下：

class Trie {

    // 树上节点类型
    private class Node{
        // 判断到该节点位置，是否是一个之前插入地字符串
        public boolean isEnd;
        // 不同字母分别对应不同地分支
        public Node[] next;

        Node()
        {
            isEnd = false;
            next = new Node[26];
        }
    }
    
    // 根节点
    private Node root;

    public Trie() {
        root = new Node();
    }
    
    public void insert(String word) {
        
        Node now = root;
        
        for (int i = 0; i < word.length(); i ++)
        {
            int pos = word.charAt(i) - 'a';

            if (now.next[pos] == null)
            {
                now.next[pos] = new Node();
            }
            now = now.next[pos];
        }
       
       //将这个节点设置为true,表示是一个合法的字符串
        now.isEnd = true;
    }
    
    public boolean search(String word) {
        Node now = root;

        for (int i = 0; i < word.length(); i ++)
        {
            int pos = word.charAt(i) - 'a';

            if (now.next[pos] == null)
                return false;
            now = now.next[pos];
        }
       
        return now.isEnd;
    }
    
    public boolean startsWith(String prefix) {
        Node now = root;

        for (int i = 0; i < prefix.length(); i ++)
        {
            int pos = prefix.charAt(i) - 'a';

            if (now.next[pos] == null)
                return false;
            now = now.next[pos];
        }

        return true;
    }
}