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"));

     }
 }