前缀树，trie树

前缀树：

　　假设一个字符串数组，“abcd”,"bcd","gef" , 构建一颗树，字母是在路径上，节点上最基本的存储的信息包括：

　　　　以这个节点结尾的 字符串的数量；

　　　　经过这个节点的字符串的数量；

一个字符串类型的数组arr1，另一个字符串类型的数组arr2；

（1）arr2中有哪些字符，是arr1中出现的？请打印

（2）arr2中有哪些字符，是作为arr1中某个字符串前缀出现的？请 打印

（3）arr2中有哪些字符，是作为arr1中某个字符串前缀出现的？请打印 arr2中出现次数最大的前缀

package my_basic.class_7;

public class Code_00_TrieTree {
    //前缀树
    public static class TrieNode{
        public int end;
        public int path;
        public TrieNode[] nexts;
        
        public TrieNode() {
            end = 0;
            path = 0;
            nexts = new TrieNode[26];   //之前没写   空指针
        }
        
    }
    
    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();
            int index = 0;
            TrieNode node = root;
            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.path++;
            }
            node.end++;
        }
        
        public int search(String word) {
            if (word == null) {
                return 0;
            }
            char[] chs = word.toCharArray();
            int index = 0;
            TrieNode node = root;
            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;
        }
        
        public void delete(String word) {
            if (word == null) {
                return;
            }
            char[] chs = word.toCharArray();
            int index = 0;
            TrieNode node = root;
            for (int i = 0; i < chs.length; i++) {
                index = chs[i] - 'a';
                if (--node.nexts[index].path == 0) {
                    node.nexts[index] = null;   //后面的节点直接删去
                    return;
                }
                node = node.nexts[index];
            }
            node.end--;
        }
        
        public int prefixNumber(String word) {
            if (word == null) {
                return 0;
            }
            char[] chs = word.toCharArray();
            int index = 1;
            TrieNode node = root;
            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.path;
        }
    }
    
    public static void main(String[] args) {
        String[] arr1 = {"abc","bcd","def","bcf"};
        String[] arr2 = {"b","a","bc"};
        Trie trie = new Trie();
        for (int i = 0; i < arr1.length; i++) {
            trie.insert(arr1[i]);
        }
        //arr2中有哪些字符，是arr1中出现的
        for (int i = 0; i < arr2.length; i++) {
            if (trie.search(arr2[i]) != 0) {
                System.out.print(arr2[i] + " ");
            }
        }
        System.out.println(" ");
        System.out.println("===================================");
        //arr2中有哪些字符，是作为arr1中某个字符串前缀出现的？
        for (int i = 0; i < arr2.length; i++) {
            if (trie.prefixNumber(arr2[i]) != 0) {
                System.out.print(arr2[i] + " ");
            }
        }
        System.out.println(" ");
        System.out.println("===================================");
        
        String res = null;
        int pre = 0;
        for (int i = 0; i < arr2.length; i++) {
            int prefixNum = trie.prefixNumber(arr2[i]);
            if (prefixNum != 0) {
                System.out.print(arr2[i] + " ");
                if(prefixNum >= pre) {
                    res = arr2[i];
                    pre = prefixNum;
                }
            }
        }
        System.out.println();
        System.out.println(res);
        
//        Trie trie = new Trie();
//        System.out.println(trie.search("zuo"));
//        trie.insert("zuo");
//        System.out.println(trie.search("zuo"));
//        trie.delete("zuo");
//        System.out.println(trie.search("zuo"));
//        trie.insert("zuo");
//        trie.insert("zuo");
//        trie.delete("zuo");
//        System.out.println(trie.search("zuo"));
//        trie.delete("zuo");
//        System.out.println(trie.search("zuo"));
//        trie.insert("zuoa");
//        trie.insert("zuoac");
//        trie.insert("zuoab");
//        trie.insert("zuoad");
//        trie.delete("zuoa");
//        System.out.println(trie.search("zuoa"));
//        System.out.println(trie.prefixNumber("zuo"));
        
        
    }
}