Slow version

word_count.cpp

#include <vector>
#include <string>
#include <unordered_map>
#include <fstream>
#include <utility>
#include <algorithm>
#include <cassert>
#include <string_view>


inline bool is_valid (char c) {
   return (65 <= c && c <= 90) || (97 <= c && c <= 122);
}


std::unordered_map<std::string, size_t> Frequencies(const std::string& ifilename) {
    std::ifstream infile(ifilename);
    assert(infile.good());
    char inchar;
    std::string acc;
    std::unordered_map<std::string, size_t> table;


    infile.get(inchar);
    while (!infile.eof()) {
        while (is_valid(inchar)) {
            if (inchar < 97) {
                inchar += 32;
            }
            acc.push_back(inchar);
            infile.get(inchar);
        }
        auto search = table.find(acc);
        if (search != table.end()) {
            ++search->second;
        } else {
            table.emplace(acc, 1);
        }
        acc.clear();
        while (infile.get(inchar) && !is_valid(inchar)) {
        }
    }
    return table;
}


void PrintInOrder(const std::unordered_map<std::string, size_t>& frequencies, const std::string& ofilename) {
    std::vector<const std::pair<const std::string, size_t>*> ordered_pairs;
    ordered_pairs.reserve(frequencies.size());
    for (auto& pair : frequencies) {
        ordered_pairs.emplace_back(&pair);
    }
    std::sort(ordered_pairs.begin(), ordered_pairs.end(),
              [](const std::pair<const std::string, size_t>* fst,
                 const std::pair<const std::string, size_t>* snd) {
                  if (fst->second == snd->second) {
                      return fst->first < snd->first;
                  }
                  return fst->second > snd->second;
              });
    std::ofstream outfile(ofilename);
    assert(outfile.good());
    for (auto pair : ordered_pairs) {
        outfile << pair->second << ' ' << pair->first << '\n';
    }
}



int main(int argc, char *argv[]) {
    assert(argc == 3);
    PrintInOrder(Frequencies(argv[1]), argv[2]);
    return 0;
}