前缀树

#include <bits/stdc++.h>

using namespace std;
const int MaxNode = 26;

struct Node {
    int end;
    int pass;
    vector<Node *> nexts;

    Node() : end(0), pass(0) {
        nexts = vector<Node *>(MaxNode, nullptr);
    };
};

class trie {
private:
    Node *root;
public:
    trie() : root(new Node()) {};

    ~trie() = default;

    //插入字符串
    void insert(string s);

    //查询字符串出现过没有，没有就返回0，有就返回这个字符串加过几次
    int search(string s);

    //查询以该字符串做前缀加了多少个
    int searchHead(string s);

    //删除某个字符串
    void Delete(string s);

};

void trie::insert(string s) {
    if (s.empty()) return;
    Node *node = root;
    node->pass++;
    int index = 0;
    for (int i = 0; i < s.size(); ++i) {
        index = s[i] - 'a';
        if (node->nexts[index] == nullptr) {
            node->nexts[index] = new Node();
        }
        node = node->nexts[index];
        node->pass++;
    }
    node->end++;
}

int trie::search(string s) {
    if (s.empty()) return 0;
    Node *node = root;
    int index = 0;
    //记录出现过几次

    for (int i = 0; i < s.size(); ++i) {
        index = s[i] - 'a';
        if (node->nexts[index] == nullptr) return 0;
        node = node->nexts[index];
    }
    return node->end;
}

int trie::searchHead(string s) {
    if (s.empty()) return 0;
    Node *node = root;
    int index = 0;
    for (int i = 0; i < s.size(); ++i) {
        index = s[i] - 'a';
        if (node->nexts[index] == nullptr) return 0;
        node = node->nexts[index];
    }
    return node->pass;
}

void trie::Delete(string s) {
    if (s.empty()) {
        cout << "error" << endl;
    }
    Node *node = root;
    node->pass--;
    int index = 0;
    for (int i = 0; i < s.size(); ++i) {
        index = s[i] - 'a';
        node = node->nexts[index];
        node->pass--;
    }
    node->end--;
}

//以上是针对字符串26个小写字母；
//如果字符扩展了到很大，我们可以用hash表来作为index(key) 和node *(value);