Ubiquitous Religions-并查集（5）

Description

There are so many different religions in the world today that it is difficult to keep track of them all. You are interested in finding out how many different religions students in your university believe in.

You know that there are n students in your university (0
< n <= 50000). It is infeasible for you to ask every student their
religious beliefs. Furthermore, many students are not comfortable
expressing their beliefs. One way to avoid these problems is to ask m (0
<= m <= n(n-1)/2) pairs of students and ask them whether they
believe in the same religion (e.g. they may know if they both attend the
same church). From this data, you may not know what each person
believes in, but you can get an idea of the upper bound of how many
different religions can be possibly represented on campus. You may
assume that each student subscribes to at most one religion.

Input

The input consists of a number of cases. Each case starts with a line
specifying the integers n and m. The next m lines each consists of two
integers i and j, specifying that students i and j believe in the same
religion. The students are numbered 1 to n. The end of input is
specified by a line in which n = m = 0.

Output

For each test case, print on a single line the case number (starting
with 1) followed by the maximum number of different religions that the
students in the university believe in.

Sample Input

10 9
1 2
1 3
1 4
1 5
1 6
1 7
1 8
1 9
1 10
10 4
2 3
4 5
4 8
5 8
0 0

Sample Output

Case 1: 1
Case 2: 7

Hint

Huge input, scanf is recommended.

#include <cstdio>
int x,y,pa[1000000];
int cha(int k)
{
    if(pa[k]!=k)
    {
        pa[k]=cha(pa[k]);
    }
    return pa[k];
}
bool bing(int x,int y)
{
    int x2=cha(x);
    int y2=cha(y);
    if(x2==y2)
        return false;
    pa[y2]=x2;
    return true;
}
void init(int n)
{
    for(int i=0; i<=n; i++)
    {
        pa[i]=i;
    }
}
int main()
{
    int n,m,k,a,b,cas=1,i;
    while(scanf("%d%d",&n,&m)&&(m+n))
    {int count=0;
    init(n);
        for(i=1; i<=m; i++)
        {
            scanf("%d%d",&a,&b);
            bing(a,b);
        }
        for(i=1;i<=n;i++)
        {
            if(pa[i]==i)//直接求根节点的个数就可以得知
                count++;
        }
        printf("Case %d: %d\n",cas++,count);
    }
    return 0;
}