查找树 trie

public class Trie {
    private int SIZE = 26;
    private TrieNode root;//字典树的根

    Trie() {//初始化字典树
        root = new TrieNode();
    }

    public int getTotal() {
        return root.num - 1;
    }

    private class TrieNode {//字典树节点
        private int num;//有多少单词通过这个节点,即节点字符出现的次数
        private TrieNode[] son;//所有的儿子节点
        private boolean isEnd;//是不是最后一个节点
        private char val;//节点的值

        TrieNode() {
            num = 1;
            son = new TrieNode[SIZE];
            isEnd = false;
        }
    }

    //建立字典树
    public void insert(String str) {//在字典树中插入一个单词
        if (str == null || str.length() == 0) {
            return;
        }
        TrieNode node = root;
        char[] letters = str.toCharArray();
        for (int i = 0, len = str.length(); i < len; i++) {
            int pos = letters[i] - 'a';
            if (node.son[pos] == null) {
                node.son[pos] = new TrieNode();
                node.son[pos].val = letters[i];
            } else {
                node.son[pos].num++;
            }
            node = node.son[pos];
        }
        root.num ++;
        node.isEnd = true;
    }

    //计算单词前缀的数量
    public int countPrefix(String prefix) {
        if (prefix == null || prefix.length() == 0) {
            return -1;
        }
        TrieNode node = root;
        char[] letters = prefix.toCharArray();
        for (int i = 0, len = prefix.length(); i < len; i++) {
            int pos = letters[i] - 'a';
            if (node.son[pos] == null) {
                return 0;
            } else {
                node = node.son[pos];
            }
        }
        return node.num;
    }

    //在字典树中查找一个完全匹配的单词.
    public boolean has(String str) {
        if (str == null || str.length() == 0) {
            return false;
        }
        TrieNode node = root;
        char[] letters = str.toCharArray();
        for (int i = 0, len = str.length(); i < len; i++) {
            int pos = letters[i] - 'a';
            if (node.son[pos] != null) {
                node = node.son[pos];
            } else {
                return false;
            }
        }
        return node.isEnd;
    }

    //前序遍历字典树.
    public void preTraverse(TrieNode node) {
        if (node != null) {
            System.out.print(node.val + (node.isEnd? " -- " :"-"));
            for (TrieNode child : node.son) {
                preTraverse(child);
            }
        }
    }

    public TrieNode getRoot() {
        return this.root;
    }

    public static void main(String[] args) {
        Trie tree = new Trie();
        String[] strs = {"banana", "band", "bee", "absolute", "acm",};
        String[] prefix = {"ba", "b", "band", "abc",};
        for (String str : strs) {
            tree.insert(str);
        }
        System.out.println(tree.getTotal());
        System.out.println(tree.has("abc"));
        tree.preTraverse(tree.getRoot());
        System.out.println();
        for (String pre : prefix) {
            int num = tree.countPrefix(pre);
            System.out.println(pre + ":" + num);
        }
    }
}