bzoj1016: [JSOI2008]最小生成树计数

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
const int mod=31011;
struct node
{
    int x,y,d;
}a[1100];
struct line
{
    int l,r,v;
}s[1100];int cnt;
int cmp(const void *xx,const void *yy)
{
    node n1=*(node *)xx;
    node n2=*(node *)yy;
    if(n1.d>n2.d)return 1;
    else if(n1.d<n2.d)return -1;
    else return 0;
}
int fa[1100];
int findfa(int x)
{
    if(x!=fa[x])return findfa(fa[x]);
    return x;
}
int sum;
void dfs(int x,int i,int k)
{
    if(i==s[x].r+1)
    {
        if(k==s[x].v)sum++;
        return ;
    }
    int fx=findfa(a[i].x),fy=findfa(a[i].y);
    if(fx!=fy)
    {
        fa[fx]=fy;
        dfs(x,i+1,k+1);
        fa[fx]=fx;fa[fy]=fy;
    }
    dfs(x,i+1,k);
}
int main()
{
    int n,m;
    scanf("%d%d",&n,&m);
    for(int i=1;i<=m;i++)scanf("%d%d%d",&a[i].x,&a[i].y,&a[i].d);
    qsort(a+1,m,sizeof(node),cmp);
    for(int i=1;i<=n;i++)fa[i]=i;
    
    int tot=0;
    for(int i=1;i<=m;i++)
    {
        if(a[i].d!=a[i-1].d)
        {
            s[cnt].r=i-1;
            cnt++;
            s[cnt].l=i;s[cnt].v=0;
        }
        
        int fx=findfa(a[i].x),fy=findfa(a[i].y);
        if(fx!=fy)
        {
            fa[fx]=fy;
            tot++;s[cnt].v++;
        }
    }
    s[cnt].r=m;
    if(tot<n-1){printf("0\n");return 0;}
    
    for(int i=1;i<=n;i++)fa[i]=i;
    int ans=1;
    for(int i=1;i<=cnt;i++)
    {
        sum=0;
        dfs(i,s[i].l,0);
        ans=(ans*sum)%mod;
        for(int j=s[i].l;j<=s[i].r;j++)
        {
            int fx=findfa(a[j].x),fy=findfa(a[j].y);
            if(fx!=fy)fa[fx]=fy;
        }
    }
    printf("%d\n",ans);
    return 0;
}