백준 6118 c++

오랜만에 풀어본 BFS문제이다.
양방향 그래프문제이고, 결과 벡터를 정렬한 후, 뒤에서부터 순회하여 계산 시간을 줄이려 했지만 그 전에 반복과정이 많아서 그런지 효과는 별로 없었다.

#include <iostream>
#include <vector>
#include <queue>
#include <algorithm>
#include <map>

using namespace std;

vector<vector<int>> barn;

void input_barn()
{
	int N, M, A, B;
	int i;

	cin >> N >> M;
	barn.resize(N + 1, vector<int>());
	for (i = 0; i < M; i++)
	{
		cin >> A >> B;
		barn[A].push_back(B);
		barn[B].push_back(A);
	}

	return;
}

bool compare(pair<int, int> A, pair<int, int> B)
{
	if (A.second == B.second)
	{
		return A.first > B.first;
	}
	else
	{
		return A.second < B.second;
	}
}

void BFS()
{
	queue <int> q;
	vector<pair<int, int>> destination;
	vector<bool> visited(barn.size() + 1, false);
	int current, next, i, j, current_cnt = 0, q_size;
	int answer, answer_distance, same_distance = 1;

	q.push(1);
	destination.push_back({ 1, 0 });
	visited[1] = true;
	while (!q.empty())
	{
		q_size = q.size();
		for (j = 0; j < q_size; j++)
		{
			current = q.front();
			q.pop();
			for (i = 0; i < barn[current].size(); i++)
			{
				next = barn[current][i];
				if (visited[next] == false)
				{
					q.push(next);
					visited[next] = true;
					destination.push_back({ next, current_cnt + 1 });
				}
			}
		}
		current_cnt++;
	}
	sort(destination.begin(), destination.end(), compare);
	/*for (pair<int, int> temp : destination)
	{
		cout << temp.first << " " << temp.second << "\n";
	}*/
	answer = destination.back().first;
	answer_distance = destination.back().second;
	for (i = destination.size() - 2; i >= 0; i--)
	{
		if (destination[i].second == destination[i + 1].second)
		{
			same_distance++;
		}
		else
		{
			break;
		}
	}
	cout << answer << " " << answer_distance << " " << same_distance << "\n";

	return;
}

void find_answer()
{
	BFS();

	return;
}

int main(void)
{
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	cout.tie(NULL);

	input_barn();
	find_answer();

	return 0;
}