Resuelve https://omegaup.com/arena/problem/estacion

estacion.cpp

#include <bits/stdc++.h>
using std::vector;

void printAnswer(int frequency, int station) {
    if (frequency < station) {
        std::cout << "adelante " << station - frequency << "\n";
    } else if (frequency > station) {
        std::cout << "atras " << frequency - station << "\n";
    }
}

void findNearestStation(int frequency, vector<int> const & stations) {
    if (frequency < stations[0]) {
        printAnswer(frequency, stations[0]);
        return;
    }
    unsigned size = stations.size();
    if (frequency > stations[size-1]) {
        printAnswer(frequency, stations[size-1]);
        return;
    }

    for (unsigned idx = 0; idx < size; idx++) {
        if (frequency == stations[idx]) {
            if (idx == 0) {
                printAnswer(stations[0], stations[1]);
                return;
            }
            if (idx == size - 1) {
                printAnswer(frequency, stations[size-2]);
                return;
            }
        }
    }

    for (int idx = 0; idx + 1 < size; idx++) {
        int left = frequency - stations[idx];
        int right = stations[idx+1] - frequency;
        if (frequency < stations[idx] || frequency > stations[idx+1]) {
            continue;
        }
        if (right <= left) {
            printAnswer(frequency, stations[idx+1]);
        } else {
            printAnswer(frequency, stations[idx]);
        }
    }
}

int main() {
    int min = 540;
    int max = 1520;
    vector<int> stations{580, 980, 1190, 1250, 1420};
    int frequency;
    std::cin >> frequency;
    if (frequency < min || frequency > max) {
        std::cout << "error\n";
    } else {
        findNearestStation(frequency, stations);
    }
    return EXIT_SUCCESS;
}