前綴樹

使用一個(gè)樹結(jié)構(gòu)記錄一組數(shù)據(jù)，數(shù)據(jù)可以是字符串?dāng)?shù)組。

public class TrieTree {
    public static class TrieNode{
        public int pass;//經(jīng)過該節(jié)點(diǎn)的字符的數(shù)量
        public int end;//以該節(jié)點(diǎn)為終的字符的數(shù)量
        public TrieNode[] nexts;

        public TrieNode(){
            pass = 0;
            end = 0;
            //nexts[0] == null 沒有走向'a'的路
            //nexts[0] 帅韧！= null 有走向'a'的路
            //...
            //nexts[25] 务唐！= null 有走向'z'的路
            nexts = new TrieNode[26]; //HashMap<Char, Node> nexts;表示很多的字符服球，
                                      // Char表示某個(gè)字符汛兜，Node表示下一個(gè)節(jié)點(diǎn)
                                      //TreeMap<Char, Node> nexts;有序表
        }

    }

    public static class Trie{
        private TrieNode root;

        public Trie(){
            root = new TrieNode();
        }

        public void insert(String word){
            if(word == null){
                return;
            }
            char[] chs = word.toCharArray();
            TrieNode node = root;
            node.pass++;//邊的end的pass++
            int index = 0;
            for (int i = 0; i < chs.length; i++) {
                index = chs[i] - 'a';
                if(node.nexts[index] == null){
                    node.nexts[index] = new TrieNode();
                }
                node = node.nexts[index];
                node.pass++;
            }
            node.end++;
        }

        //刪除前綴樹中的某個(gè)單詞,刪一個(gè)
        public void delete(String word){
            if(search(word) != 0){
                char[] chs = word.toCharArray();
                TrieNode node = root;
                node.pass--;
                int index = 0;
                for (int i = 0; i < chs.length; i++) {
                    index = chs[i] - 'a';
                    if(--node.nexts[index].pass == 0){
                        node.nexts[index] = null;
                        return;
                    }
                    node = node.nexts[index];
                }
                node.end--;
            }
        }

        //查看前綴樹里有多少word
        public int search(String word){
            if(word == null){
                return 0;
            }
            char[] chs = word.toCharArray();
            TrieNode node = root;
            int index = 0;
            for (int i = 0; i < chs.length; i++) {
                index = chs[i] - 'a';
                if(node.nexts[index] == null){
                    return 0;
                }
                node = node.nexts[index];
            }
            return node.end;
        }
        //所有加入的字符串中，有幾個(gè)是以pre這個(gè)字符串為前綴的
        public int prefixNumber(String pre){
            if(pre == null){
                return 0;
            }
            char[] chs = pre.toCharArray();
            TrieNode node = root;
            int index = 0;
            for (int i = 0; i < chs.length; i++) {
                index = chs[i] - 'a';
                if(node.nexts[index] == null){
                    return 0;
                }
                node = node.nexts[index];
            }
            return node.pass;
        }
    }
}