HDU 2120 Ice_cream's world I

Ice_cream's world I
Time Limit:1000MS     Memory Limit:32768KB     64bit IO Format:%I64d
& %I64u
Submit Status Practice HDU
2120

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
4000
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

#include<stdio.h>
#include<string.h>
using namespace std;
const int M=10005;
int pre[M];
int cnt;
int find(int p)
{
while(p!=pre[p])
p=pre[p];
return p;
}
void merge(int x,int y)
{
int fx=find(x);
int fy=find(y);
if(fx!=fy)
pre[fy]=fx;
else
cnt++;
}
int main()
{
int n,m,a,b,i;
while(~scanf("%d%d",&n,&m))
{
cnt=0;
for(i=0;i<M;i++)
pre[i]=i;
while(m--)
{
scanf("%d%d",&a,&b);
merge(a,b);
}
printf("%d\n",cnt);
}
}