1021. Deepest Root

考察连通分量个数，用搜索或并查集，并查集效率较高；

求最深的树根节点，用dfs

// 1021. Deepest Root.cpp: 主项目文件。

#include "stdafx.h"
#include <cstdio>
#include <cstring>
#include <vector>
using namespace std;

const int N=10003;
bool used[N];
vector<int> edge[N];
vector<int> needRoot;
int maxLevel,tLevel,n;

void dfs(int cur,int level){
	used[cur]=true;
	if(level>=tLevel)
		tLevel=level;
	for(vector<int>::iterator ite=edge[cur].begin();ite!=edge[cur].end();ite++){
		if(!used[*ite]){
			dfs(*ite,level+1);
		}
	}
}

int countTrees(){
	int cnt=0;
	tLevel=-1;
	memset(used,0,sizeof(used));
	for(int i=1;i<=n;i++){
		if(!used[i]){
			dfs(i,1);
			++cnt;
		}
	}
	return cnt;
}

void computeDeepestRoot(){
	maxLevel=-1;
	for(int i=1;i<=n;i++){
		memset(used,0,sizeof(used));
		tLevel=-1;
		dfs(i,1);
		if(tLevel>maxLevel){
			maxLevel=tLevel;
			needRoot.clear();
			needRoot.push_back(i);
		}
		else if(tLevel==maxLevel)
			needRoot.push_back(i);
	}
	for(vector<int>::iterator ite=needRoot.begin();ite!=needRoot.end();++ite)
		printf("%d\n",*ite);
}

int main()
{
	scanf("%d",&n);
	for(int i=1;i<n;i++){
		int u,v;
		scanf("%d%d",&u,&v);
		edge[u].push_back(v);
		edge[v].push_back(u);
	}
	int connectedCnt=countTrees();
	if(connectedCnt>1)
		printf("Error: %d components\n",connectedCnt);
	else
		computeDeepestRoot();
    return 0;
}