main.cpp

#include <cstdio>
#include <utility>
#include <cmath>
#include <string>
#include <vector>
#include <algorithm>

using namespace std;

struct TrackingEvent {
    string uuid;
    double lat;
    double lon;

    TrackingEvent(string uuid, double lat, double lon) : uuid(std::move(uuid)), lat(lat), lon(lon) {}
};

struct Airport {
    string iata_code;
    double lat;
    double lon;

    Airport(string iata_code, double lat, double lon) : iata_code(std::move(iata_code)), lat(lat), lon(lon) {}
};

const double PI_DIV_180 = M_PI / 180.0;

inline double to_radians(const double& degree) { return degree * PI_DIV_180; }

double haversine(double lat1, double lon1, double lat2, double lon2) {
    double phi1 = to_radians(lat1);
    double phi2 = to_radians(lat2);

    double delta_phi = to_radians(lat2 - lat1);
    double delta_lambda = to_radians(lon2 - lon1);

    double sinLat2 = sin(delta_phi / 2);
    double sinLon2 = sin(delta_lambda / 2);

    double a = sinLat2 * sinLat2 + cos(phi1) * cos(phi2) * sinLon2 * sinLon2;

    double c = 2 * atan2(sqrt(a), sqrt(1 - a));

    return 6371e3 * c; // distance in meters
}

int main() {
    string iata_code, uuid;
    double lat, lon;

    // airports

    FILE* airports_file = fopen("data/airports.csv", "r");
    vector<Airport> airports;

    fscanf(airports_file, "%s", new string); // header
    while (fscanf(airports_file, "%s,%lf,%lf", iata_code, &lat, &lon) == 3) {
        airports.push_back(Airport(iata_code, lat, lon));
    }
    fclose(airports_file);

    // events

    FILE* events_file = fopen("data/events.csv", "r");
    vector<TrackingEvent> events;

    fscanf(events_file, "%s", new string); // header
    while (fscanf(airports_file, "%s,%lf,%lf", uuid, &lat, &lon) == 3) {
        events.push_back(TrackingEvent(uuid, lat, lon));
    }
    fclose(events_file);

    // match

    FILE* out_file = fopen("data/out.csv", "w+");

    for (const auto& event:events) {
        const auto& nearestAirport = std::min_element(
                airports.begin(),
                airports.end(),
                [](const Airport& a1, const Airport& a2) {
                    return haversine(a1.lat, a1.lon, event.lat, event.lon) <
                           haversine(a2.lat, a2.lon, event.lat, event.lon);
                }
        );
        fprintf(out_file, "%s,%s\n", event.uuid, nearestAirport->iata_code);
    }

    fclose(out_file);
    return 0;
}