ExploreKeyWords_v2

#include <functional>
#include <iostream>
#include <map>
#include <set>
#include <vector>
#include <sstream>
#include <string>

#include <future>
#include <algorithm>
#include <execution>

using namespace std;

struct Stats {
    map<string, int> word_frequences;

    void operator+=(const Stats& other) {
        // сложить частоты
        for_each(execution::par, other.word_frequences.begin(), other.word_frequences.end(),
            [this](const pair<const string&, int>& pair) {
                word_frequences[pair.first] += pair.second;
            });
    }
};

using KeyWords = set<string, less<>>;

vector<string_view> SplitIntoWords(string_view text) {
    vector<string_view> result;
    text.remove_prefix(min(text.find_first_not_of(" "), text.size()));
    while (!text.empty()) {
        size_t position_first_space = text.find(' ');
        string_view tmp_substr = text.substr(0, position_first_space);
        result.push_back(tmp_substr);
        text.remove_prefix(tmp_substr.size());
        text.remove_prefix(min(text.find_first_not_of(" "), text.size()));
    }
    return result;
}

bool CheckPrintSymbols(string_view word) {
    bool check_result = true;
    for_each(execution::par, word.begin(), word.end(), [&check_result](auto symbol) {
        if (!isprint(symbol)) {
            check_result = false;
        }
    });
    return check_result;
}

Stats ExploreKeyWords(const KeyWords& key_words, istream& input) {
    Stats statistics;
    vector<string> content;
    while (!input.eof()) {
        string text;
        getline(input, text);
        if (text.empty()) {
            break;
        }
        content.push_back(text);
    }
    for (string_view text : content) {
        if (!CheckPrintSymbols(text)) {
            statistics.word_frequences.clear();
            break;
        }
        future<void> test = async([&key_words, &statistics, text] {
            Stats stats_one_string;
            vector<string_view> words = SplitIntoWords(text);
            for (vector<string_view>::iterator it = words.begin() + 1; it != words.end() - 1; ++it) {
                if (key_words.count(*it)) {
                    stats_one_string.word_frequences[string(*it)]++;
                }
            }
            statistics += stats_one_string;
        });
    }
    return statistics;
}

int main() {
    const KeyWords key_words = { "yangle", "rocks", "sucks", "all" };

    stringstream ss;
    ss << "this new yangle service really rocks\n";
    ss << "It sucks when yangle isn't available\n";
    ss << "10 reasons why yangle is the best IT company\n";
    ss << "yangle rocks others suck\n";
    ss << "Goondex really sucks, but yangle rocks. Use yangle\n";

    for (const auto& [word, frequency] : ExploreKeyWords(key_words, ss).word_frequences) {
        cout << word << " " << frequency << endl;
    }

    return 0;
}