ИИ - Алгоритми 2021 задачи за решавање: Боксерски турнир

#include <bits/stdc++.h>
using namespace std;
enum boxer_colour // the colour
{
    UNDEFINED, // non-visited
    RED,
    BLUE
};
struct boxer // a boxer point
{
    boxer_colour colour;
    vector <int> boxing_with;
    boxer()
    {
        colour = UNDEFINED;
        return;
    }
};
boxer_colour opposite(boxer_colour c)
{
    switch (c)
    {
    case RED:
        return BLUE;
    case BLUE:
        return RED;
    case UNDEFINED:
        return UNDEFINED;
    default:
        return UNDEFINED;
    }
}
int main()
{
    int boxers_count, edges; // size of boxers array
    cin >> boxers_count >> edges;
    vector <boxer> boxers(boxers_count); // boxers
    for (int i = 0; i < edges; i++) // input edges
    {
        int a, b;
        cin >> a >> b;
        boxers[a].boxing_with.push_back(b);
        boxers[b].boxing_with.push_back(a);
    }
    queue <int> bfs_queue; // BFS queue
    bfs_queue.push(0); // add boxer 0 to BFS queue
    boxers[0].colour = RED;
    while (!bfs_queue.empty()) // BFS
    {
        int boxer_index = bfs_queue.front(); // get check index for boxer
        bfs_queue.pop();
        for (int i = 0; i < boxers[boxer_index].boxing_with.size(); i++) // check all edges connecting to boxer
        {
            if (boxers[boxers[boxer_index].boxing_with[i]].colour == boxers[boxer_index].colour)
            {
                cout << "NE"; // two neighbour boxers have same pants colour
                return 0;
            }
            if (boxers[boxers[boxer_index].boxing_with[i]].colour == UNDEFINED)
            {
                boxers[boxers[boxer_index].boxing_with[i]].colour = opposite(boxers[boxer_index].colour);
                bfs_queue.push(boxers[boxer_index].boxing_with[i]); // colour with opposite colour
            }
        }
    }
    cout << "DA"; // all pants are given
    return 0;
}