用三叉树实现高效字符查找

package com.zerob13.TernaryTree;
/**
 *
 * @author yanglingfeng
 */
public class TernaryTree {
    private class Node {
        char m_char;
        Node left, right, middle;
        boolean end;
        public Node(char ch, boolean e) {
            m_char = ch;
            end = e;
        }
        public Node(char ch, boolean e, Node leftc, Node rightc, Node middlec) {
            m_char = ch;
            end = e;
            left = leftc;
            right = rightc;
            middle = middlec;
        }
    }
    private Node root;
    private int count;
    /**
     * 初始化三叉树
     */
    public TernaryTree() {
        clear();
    }
    /**
     * 清除三叉树
     */
    public final void clear() {
        root = null;
        count = 0;
    }
    /**
     * 插入一个字符串
     * @param s
     */
    public void insert(String s) {
        root = insert(root, s, 0);
    }
    /**
     * 返回三叉树大小
     * @return
     */
    public int size() {
        return count;
    }
    /**
     * 返回是否能够找到字符串s
     * @param s
     * @return boolean
     */
    public boolean contains(String s) {
        return search(root, s, 0) != null;
    }
    private Node search(Node ref, String s, int pos) {
        if (ref == null) {
            return null;
        } else {
            int cmp = s.charAt(pos) - ref.m_char;
            if (cmp < 0) {
                return search(ref.left, s, pos);
            } else if (cmp > 0) {
                return search(ref.right, s, pos);
            } else {
                if (1 + pos == s.length()) {
                    if (ref.end) {
                        return ref;
                    } else {
                        return null;
                    }
                }
                return search(ref.middle, s, pos + 1);
            }
        }
    }
    private Node insert(Node ref, String s, int i) {
        if (ref == null) {
            count++;
            ref = new Node(s.charAt(i), false);
        }
        int cmp = s.charAt(i) - ref.m_char;
        if (cmp < 0) {
            ref.left = insert(ref.left, s, i);
        } else if (cmp > 0) {
            ref.right = insert(ref.right, s, i);
        } else {
            if (i + 1 == s.length()) {
                ref.end = true;
            } else {
                ref.middle = insert(ref.middle, s, i + 1);
            }
        }
        return ref;
    }
}