poj1308 并查集

比较恶心

1: 0 0 空树是一棵树
2: 1 1 0 0 不是树
3: 1 2 1 2 0 0 不是树...
4: 1 2 2 3 4 5 不是树  森林不算是树
5: 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 1  错
6: 1 2 2 1 0 0 也是错误的

#include<stdio.h>
#include<string.h>
int pa[],a[],b[],n,in[],map[],hash[];
void init()
{
    for(int i=;i<=n;i++)
    {
        pa[i]=i;
    }
}
int find(int x)
{
    if(x!=pa[x])
        pa[x]=find(pa[x]);
    return pa[x];
}
int main()
{
    int i,j,flag,ff=;
    while(scanf("%d%d",&a[],&b[])!=EOF)
    {
        j=;
        memset(hash,,sizeof(hash));
        memset(map,,sizeof(map));
        memset(in,,sizeof(in));
        if(!hash[a[]])
            map[j++]=a[];
        if(!hash[b[]])
            map[j++]=b[];
        if(a[]==&&b[]==)
        {
            printf("Case %d is a tree.\n",++ff);
            continue;
        }
        n=;
        flag=;
        if(a[]<&&b[]<)
            break;
        in[a[]]++,in[b[]]++;
        if(a[] > n) n = a[];
        if(b[] > n) n = b[];
        i=;
        while()
        {
            i++;
            scanf("%d %d",&a[i],&b[i]);
            if(a[i]==&&b[i]==)
                break;
            if(!hash[a[i]])
            {
                hash[a[i]]=;
                map[j++]=a[i];
            }
            if(!hash[b[i]])
            {
                map[j++]=b[i];
                hash[b[i]]=;
            }
            if(a[i] > n) n = a[i];
            if(b[i] > n) n = b[i];
        }
        int num=j;
        //for(j=0;j<num;j++)
        //    printf("%d ",map[j]);
        //printf("\n");
        int len=i;
        init();
        for(i=;i<len;i++)
        {
            int x,y;
            x=find(a[i]);
            y=find(b[i]);
            if(x!=y)
            {
                pa[x]=y;
            }
            else
                flag=;
        }
        int ans=;
        for(i=;i<num;i++)
        {
            if(pa[map[i]]==map[i])
            {
                ans++;
            }
        }
        if(ans>)
            flag=;
        if(flag)
            printf("Case %d is a tree.\n",++ff);
        else
            printf("Case %d is not a tree.\n",++ff);
    }
}