Trie树

　　Trie树形状如图-->

应用场景-->

典型应用是用于统计，排序和保存大量的字符串(不仅限于字符串)，经常被搜索引擎系统用于文本词频统计

代码-->java

public class Main {

     private int SIZE = 26;
     private TrieNode root;
    public static void main(String[] args) {
        

        
        Main main = new Main();
        String[]strs= {"banana","band","bee","absolute","acm",};
        String[]prefix= {"ba","b","band","abc",};
        for (String str : strs) {
            main.insert(str);
        }

        main.preTraverse(main.root);
        System.out.println("
"+main.has("abc"));
        if (main.has("abc")) {
            System.out.println(main.has("abc"));
        } else {
            main.insert("abc");
            System.out.println(main.has("abc"));
        }
    }
    public Main() {
        root = new TrieNode();
    }
    public void insert(String str) {
        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.sonNodes[pos] == null) {
                node.sonNodes[pos] = new TrieNode();
                node.sonNodes[pos].val = letters[i];
            } else {
                node.sonNodes[pos].num++;
            }
            node = node.sonNodes[pos];
        }
        node.isEnd = true;
    }
    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.sonNodes[pos]!=null) {
                node = node.sonNodes[pos];
            } else {
                return false;
            }
        }
        return node.isEnd;
    }
    public void preTraverse(TrieNode node)
    {
        if(node!=null)
        {
            System.out.print(node.val+"-");
            for(TrieNode child:node.sonNodes)
            {
                preTraverse(child);
            }
        }
    }
    
    class TrieNode {
        private int num;
        private TrieNode[] sonNodes;
        private boolean isEnd;
        private char val;
        TrieNode() {
            num=1;
            sonNodes = new TrieNode[SIZE];
            isEnd = false;
        }
    }
}

代码-->c#

#include<iostream>
#include<string>
using namespace std;

struct trieNode{
    int count;//统计单词前缀出现的次数
    trieNode* next[26];//指向各子树的指针
    bool exit;//标记该结点处是否构成单词

    trieNode():count(0),exit(false){
        for (int i = 0; i < 26; i++){
            next[i] = NULL;
        }
    }
};


void trieInsert(trieNode* root, string &word){
    trieNode *node = root;
    int id;
    int len = word.size();
    int i = 0;
    while (i < len){
        id = word[i]-'a';
        if (node->next[id] == NULL){
            node->next[id] = new trieNode();
        }
        
        node = node->next[id];
        node->count += 1;

        i++;
    }
    node->exit = true;//单词结束，可以构成一个单词
}

int trieSearch(trieNode*root, string &word){

    trieNode* node = root;
    int len = word.size();
    int i = 0;
    while (i < len){
        int id = word[i] - 'a';
        if (node->next[id] != NULL){
            node = node->next[id];
            i++;
        }
        else{
            return 0;
        }
    }

    return node->count;
}


int main()
{
    trieNode *root = new trieNode();

    string word;
    int flag = false;

    while (getline(cin, word)){
        if (flag){
            cout << trieSearch(root, word) << endl;
        }
        else{
            if (!word.empty()){
                trieInsert(root, word);
            }
            else{
                flag = true;
            }
            
        }
    }

    return 0;
}