TravelCost.java

import java.util.ArrayList;
import java.util.List;

public class TravelCost {

    private final static Integer[][] participants = {{500, 700}, {200, 600}, {400, 500}, {600, 200}, {500,300}};
    private final static int cityAmount = participants[0].length;
    private final static List<Integer> result = new ArrayList<>();

    public static void main(String[] args) {
        sum(0, 0, 0, 0);
        System.out.printf(String.valueOf(result));
    }

    private static boolean sum(int fee, int i, int sf, int na) {
        if (i == participants.length) {
            return result.add(fee);
        }
        for (int p = 0; p < cityAmount; p++) {
            int capacity = (int) Math.ceil(participants.length / 2.0);
            if ((sf == capacity && p == 0) ||
                (na == capacity && p == 1)) {
                continue;
            }
            sum(fee + participants[i][p], i + 1, p == 0 ? sf + 1 : sf, p == 0 ? na : na + 1);
        }
        return true;
    }
}