Airport passengers estimation by flight timetable

#include <iostream>
#include <fstream>
#include <vector>
#include <utility>
#include <algorithm>

const int OPEN = 0;
const int CLOSE = 1;

const int PASSENGERS = 180;
const int INTERVAL_LENGTH = 60;
const double INTENSITY = ((double)PASSENGERS) / INTERVAL_LENGTH;

struct Event {

    int type, minutes;

    Event(int type, int minutes) : type(type), minutes(minutes) {}

    bool operator < (const Event& b) {
        return (minutes < b.minutes || minutes == b.minutes && type == CLOSE && b.type == OPEN);
    }

};

int timeToMinutes(int h, int m) {
    return h * 60 + m;
}

void minutesToTime(int minutes, int& h, int& m) {
    h = minutes / 60;
    m = minutes % 60;
}

int main() {
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
    int hours, minutes;
    std::vector<Event> events;
    while (scanf("%d:%d", &hours, &minutes) == 2) {
        int intervalEnd = timeToMinutes(hours, minutes) - 30,
            intervalBegin = intervalEnd - INTERVAL_LENGTH;
        events.push_back(Event(OPEN, intervalBegin));
        events.push_back(Event(CLOSE, intervalEnd));
    }
    std::sort(events.begin(), events.end());
    double currentIntensity = 0;
    std::vector<std::pair<int, double>> changes; // пара: минуты, интенсивность
    for (auto& it : events) {
        if (it.type == OPEN) {
            currentIntensity += INTENSITY;
        } else {
            currentIntensity -= INTENSITY;
        }
        if (changes.empty() || it.minutes > changes.back().first) {
            changes.push_back(std::make_pair(it.minutes, currentIntensity));
        } else {
            changes.back().second = currentIntensity;
        }
    }
    for (auto& it : changes) {
        int hours, minutes;
        double currentIntensity = it.second;
        minutesToTime(it.first, hours, minutes);
        printf("%02d:%02d %.2lf\n", hours, minutes, currentIntensity);
    }
    return 0;
}