HDU 2120 Ice_cream's world I

Description

ice_cream's world is a rich country, it has many fertile lands. Today, the queen of ice_cream wants award land to diligent ACMers. So there are some watchtowers are set up, and wall between watchtowers be build, in order to partition the ice_cream’s world. But how many ACMers at most can be awarded by the queen is a big problem. One wall-surrounded land must be given to only one ACMer and no walls are crossed, if you can help the queen solve this problem, you will be get a land.

 

Input

In the case, first two integers N, M (N<=1000, M<=10000) is represent the number of watchtower and the number of wall. The watchtower numbered from 0 to N-1. Next following M lines, every line contain two integers A, B mean between A and B has a wall(A and B are distinct). Terminate by end of file.

 

Output

Output the maximum number of ACMers who will be awarded. 
One answer one line.

 

Sample Input

     
     
     
     

      
      
      
      8 10
0 1
1 2
1 3
2 4
3 4
0 5
5 6
6 7
3 6
4 7 
     
     
     
     

 

Sample Output

     
     
     
     

      
      
      
      3 
     
     
     
     

 

原谅我其实看不懂题。

题意：问在一个图中，有几个环；（应该是这样）

小希同学那道题中判断环的思想，直接ans++；

AC代码：

#include <bits/stdc++.h>
using namespace std ;
int n , m , pre[2000],vis[2000],ans;
int find ( int x )
{
	if(x!=pre[x])
	return pre[x]=find(pre[x]);
	return x ;
}
void mix(int x , int y )
{
	int dx = find(x);
	int dy = find(y);
	if(dx!=dy)
	{
		pre[dy]=dx;
	}
	else ans++;
}
int main()
{
	while(cin>>n>>m)
	{
		ans = 0 ;
		for(int i = 0 ; i<n;i++)
		{
			vis[i]=0;
			pre[i]=i;
		}
		for(int i= 0 ; i < m ; i++)
		{
			int a , b ;
			cin>>a>>b;
			mix(a,b);
		}
		cout<<ans<<endl;
	}
	return 0 ;
}