Регулярные выражения

#include <string>
#include <iostream>
#include <map>
#include <regex>
#include <algorithm>
 
int main(int argc, char** argv) {
    const std::regex re(""GET(? : https ? ://.+?/)?(.+?\\.mp3) "
        "HTTP/1\\.[01]" \\d{ 3 } (\\d + )");
  std::map<std::string, std::pair<long, long>> stat;
  for(std::string line; std::getline(std::cin, line); ) {
    std::smatch match;
    if(std::regex_search(line, match, re)) {
      const std::string fname = match[1];
      long size = atol(match[2].str().c_str());
      auto it = stat.find(fname);
      if(it == stat.end()) { // not found
        stat[fname] = std::pair<long, long>(size, size);
      } else {
        auto pair = stat[fname];
        long sum = pair.first;
        long max = pair.second;
        sum += size;
        max = std::max(max, size);
        stat[fname] = std::pair<long, long>(sum, max);
      }
    }
  }
 
  for(auto& it: stat) {
    auto& key = it.first;
    auto& value = it.second;
    long sum = value.first;
    long max = std::max(value.second, 1L); // avoid division by zero
    double downloads = (double)sum / (double)max;
    std::cout << "Key: " << key << " downloads: " << downloads
              << " (max size: " << max << ")" << std::endl;
  }
}