PAT 1021. Deepest Root (25)

//1021. Deepest Root (25)
//第二个case是测试N =0 的情况

#include <iostream>
#include <algorithm>
#include <queue>
#include <vector>
using namespace std;

vector<int> Road[10005];
int VisitedNum = 0;
bool visit[10005] = {false};
int N;
queue<int> q;
int currlen = 0;
int maxlen = 0;

vector<int> result;

void dfs(int curr)
{
	int i;
	if (currlen >= maxlen)
	{
		if (currlen == maxlen)
		{
			if (find(result.begin(), result.end(), curr)==result.end())
			{
				result.push_back(curr);
			}
		}
		else
		{
			maxlen = currlen;
			result.pop_back();
			if (find(result.begin(), result.end(), curr)==result.end())
			{
				result.push_back(curr);
			}
		}
	}
	for (i = 1;i<=N;i++)
	{
		if (i!=curr && /*Road[i][curr] == true*/ find(Road[curr].begin(), Road[curr].end(), i)!=Road[curr].end() && visit[i] == false)
		{
			visit[curr] = true;
			VisitedNum++;
			currlen++;
			dfs(i);
			visit[curr] = false;
			VisitedNum--;
			currlen--;
		}
	}
}


int main()
{
	scanf("%d", &N);

	int i;
	int n1, n2;
	for (i = 1;i<N;i++)
	{
		scanf("%d %d", &n1, &n2);
		Road[n1].push_back(n2);
		Road[n2].push_back(n1);
	}

	if (N == 1)
	{
		printf("1\n");
		return 0;
	}
	//BFS

	int componentsnum = 0;

	int j;
	for ( j = 1;j<=N;j++)
	{
		if (visit[j] == true)
		{
			continue;
		}

		q.push(j);

		while(!q.empty())
		{
			int topnum = q.front();
			q.pop();
			for( i = 0 ;i<Road[topnum].size();i++)
			{
				if (visit[Road[topnum][i]] == false)
				{		
					q.push(Road[topnum][i]);
					visit[Road[topnum][i]] = true;
				}

			}
		}

		if (q.empty())
		{
			componentsnum++;
		}

	}

	if (componentsnum != 1)
	{
		printf("Error: %d components", componentsnum);
		return 0;
	}

	fill(visit, visit+N+1, false);
	VisitedNum = 1;
	visit[1]=true;
	dfs(1);  

	if (result.size()> 1)
	{
		sort(result.begin(), result.end());
		for (i = 0;i<result.size();i++)
		{
			printf("%d\n", result[i]);
		}
		return 0;
	}

	fill(visit, visit+N+1, false);
	VisitedNum = 1;
	visit[result[0]] = true;
	currlen = 0;
	//maxlen = 0;
 	dfs(result[0]);

	sort(result.begin(), result.end());
	for (i = 0;i<result.size();i++)
	{
		printf("%d\n", result[i]);
	}
	return 0;
}