1021. Deepest Root (25) -- 并查集 dfs

1021. Deepest Root (25)

A graph which is connected and acyclic can be considered a tree. The height of the tree depends on the selected root. Now you are supposed to find the root that results in a highest tree. Such a root is calledthe deepest root.

Input Specification:

Each input file contains one test case. For each case, the first line contains a positive integer N (<=10000) which is the number of nodes, and hence the nodes are numbered from 1 to N. Then N-1 lines follow, each describes an edge by given the two adjacent nodes' numbers.

Output Specification:

For each test case, print each of the deepest roots in a line. If such a root is not unique, print them in increasing order of their numbers. In case that the given graph is not a tree, print "Error: K components" where K is the number of connected components in the graph.

Sample Input 1:

5
1 2
1 3
1 4
2 5

Sample Output 1:

3
4
5

Sample Input 2:

5
1 3
1 4
2 5
3 4

Sample Output 2:

Error: 2 components

---

http://www.patest.cn/contests/pat-a-practise/1021

ac关键:进行多次的DFS,set<>集合应用

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<iostream>
#include<string>
#include<vector>
#include<set>


using namespace std;


const int INF=0x7fffffff;
const int N=10005;


int n;


vector<int> vt[N];


int fa[N];
int Find(int x){
	if(x==fa[x])
		return x;
	return fa[x]=Find(fa[x]);
}


void Merge(int x,int y){
	int xx=Find(x);
	int yy=Find(y);
	fa[yy]=xx;
}


int maxHeight;
int Height[N];
bool vis[N];


int tmpMaxId;




void DFS(int root,int h){
	if(vis[root])
		return;
	vis[root]=true;
	Height[root]=h;
	if(h>maxHeight)
	{
		maxHeight=h;
		tmpMaxId = root;
	}
	int len=vt[root].size();
	for(int i=0;i<len;i++){
		int v=vt[root][i];
		DFS(v,h+1);
	}
}


int main(){
	//freopen("in.txt","r",stdin);
	while(scanf("%d",&n)!=EOF){
		int i;
		int u,v;
		for(i=1;i<=n;i++){
			fa[i]=i;
			vt[i].clear();
		}
		for(i=0;i<n-1;i++){
			scanf("%d%d",&u,&v);
			vt[u].push_back(v);
			vt[v].push_back(u);
			if(Find(u)!=Find(v))
				Merge(u,v);
		}
		set<int> st;
		for(i=1;i<=n;i++)
			st.insert(Find(i));
		int stlen=st.size();
		if(stlen>1)
			printf("Error: %d components\n",stlen);
		else{
			for(i=1;i<=n;i++)
				vis[i]=false;
			maxHeight=0;
			tmpMaxId = -1;
			DFS(1,1);
			//
			vector<int> vans;
		/*	for(i=1;i<=n;i++){
				if(Height[i]==maxHeight)
					vans.push_back(i);
			}*/
			int lenv=vans.size();
			/*for(i=0;i<lenv;i++){
				for(int j=1;j<=n;j++)
					vis[j]=false;
				DFS(vans[i],1);
			}*/


			maxHeight = -1;
			for(int j=1;j<=n;j++)
				vis[j]=false;
			DFS(tmpMaxId, 1);


			int tmpMax=maxHeight;
			vans.clear();
			for(i=1;i<=n;i++){
				maxHeight=0;
				for(int j=1;j<=n;j++)
					vis[j]=false;
				DFS(i,1);
				if(maxHeight==tmpMax){
					vans.push_back(i);
				}
			}


			lenv=vans.size();
			for(int i=0;i<lenv;i++)
				cout<<vans[i]<<endl;
		}
	}//end while
	return 0;
}