四个词各出现几次

四个要找的词 he、she、his、hers，一段文本 ushershishe（11 个字符，下标从 0 起）。

按 WORDS 里的顺序，输出四个词各自的出现次数：

#include <iostream>
#include <string>
#include <vector>
using namespace std;
#include <algorithm>
#include <map>
#include <utility>

const vector<string> WORDS = {"he", "she", "his", "hers"};
const string TXT = "ushershishe";

struct TNode {
    map<char, TNode*> next;
    string word;          // 不空：有一个词在这里结束
};

TNode* build(const vector<string>& words) {
    TNode* root = new TNode();
    for (const string& w : words) {
        TNode* node = root;
        for (char ch : w) {
            if (!node->next.count(ch)) node->next[ch] = new TNode();
            node = node->next[ch];
        }
        node->word = w;
    }
    return root;
}

vector<pair<int, string>> scan(TNode* root, const string& txt) {
    vector<pair<int, string>> hits;
    for (int i = 0; i < (int)txt.size(); i++) {
        TNode* node = root;
        for (int j = i; j < (int)txt.size(); j++) {
            auto it = node->next.find(txt[j]);
            if (it == node->next.end()) break;
            node = it->second;
            if (!node->word.empty()) hits.push_back({i, node->word});
        }
    }
    sort(hits.begin(), hits.end());
    return hits;
}

int main() {
    auto hits = scan(build(WORDS), TXT);
    for (size_t k = 0; k < WORDS.size(); k++) {
        int c = 0;
        for (auto& h : hits) if (h.second == WORDS[k]) c++;
        cout << (k ? "/" : "") << c;
    }
    cout << endl;
}

（本题用 g++ -std=c++17 -O0 编译。）