hdu 5971 ：Wrestling Match（DFS染色）

http://acm.hdu.edu.cn/showproblem.php?pid=5971

Problem Description

Nowadays, at least one wrestling match is held every year in our country. There are a lot of people in the game is "good player”, the rest is "bad player”. Now, Xiao Ming is referee of the wrestling match and he has a list of the matches in his hand. At the same time, he knows some people are good players,some are bad players. He believes that every game is a battle between the good and the bad player. Now he wants to know whether all the people can be divided into "good player" and "bad player".

Input

Input contains multiple sets of data.For each set of data,there are four numbers in the first line:N (1 ≤ N≤ 1000)、M(1 ≤M ≤ 10000)、X,Y(X+Y≤N ),in order to show the number of players(numbered 1toN ),the number of matches,the number of known "good players" and the number of known "bad players".In the next M lines,Each line has two numbersa, b(a≠b) ,said there is a game between a and b .The next line has X different numbers.Each number is known as a "good player" number.The last line contains Y different numbers.Each number represents a known "bad player" number.Data guarantees there will not be a player number is a good player and also a bad player.

Output

If all the people can be divided into "good players" and "bad players”, output "YES", otherwise output "NO".

Sample Input

5 4 0 0
1 3
1 4
3 5
4 5
5 4 1 0
1 3
1 4
3 5
4 5
2

Sample Output

NO
YES

题意分析：

有n个人和m场比赛，每个人都是好球员或者坏球员，每场比赛获胜的是好球员，失败的是坏球员，已知有x个好球员和y个好球员，问能不能把这n个人完全分为好球员和坏球员，一个人只能有一个称号。

解题思路：

DFS染色，由于不是连通图，所以对每一个好球员和每一个坏球员染色，把与之比赛的人染成另一种颜色，之后还要对没有访问过的球员染色，期间如果遇到染色颜色不同的既可以结束， 如果一个人没有发生比赛，而且已知的好坏球员中都没有他，也是染色失败。

#include <stdio.h>
#include <string.h>
#include <vector>
#define N 1020
using namespace std;
vector<int>e[N];
int n, m, temp, color[N], a[N], b[N];
bool book[N];
int dfs(int u)
{
	if(temp==0)
		return 0;
	book[u]=true;
	for(int v=0; v<e[u].size(); v++){
		int f=e[u][v];
		if(color[f]==color[u]){
			temp=0;
			return 0;
		}
		if(color[u]==1)
			color[f]=2;
		else
			color[f]=1;
		if(book[f]==false)
			dfs(f);
	}
	return 1;
}
void init()
{
	int x, y, u, v;
	memset(color, 0, sizeof(color));
	memset(book, false, sizeof(book));
	scanf("%d%d", &x, &y);
	for(int i=1; i<=n; i++)
		e[i].clear();
	while(m--)
	{
		scanf("%d%d", &u, &v);
		e[u].push_back(v);
		e[v].push_back(u);
	}
	for(int i=1; i<=x; i++){
		scanf("%d", &a[i]);
		color[a[i]]=1;
	}
	for(int i=1; i<=y; i++){
		scanf("%d", &b[i]);
		color[b[i]]=2;
	}
	temp=1;
	for(int i=1; i<=x; i++)
		if(!dfs(a[i]))
		{
			printf("NO
");
			return ;	
		} 
	for(int i=1; i<=y; i++)
		if(!dfs(a[i]))
		{
			printf("NO
");
			return ;
		}
	for(int i=1; i<=n; i++)
	{
		if(!color[i]){
			if(!e[i].size())
			{
				printf("NO
");
				return ;
			}
			color[i]=1;
			if(!dfs(i))
			{
				printf("NO
");
				return ;
			}
		}
	}
	printf("YES
");
}
int main()
{
	while(scanf("%d%d", &n, &m)!=EOF){
		init();
	}
	return 0;
}