[bzoj1016]：[JSOI2008]最小生成树计数

#include<cstdio>
#include<cstring>
#include<iostream>
#include<cmath>
#include<algorithm>
#include<cstdlib>
#define ll long long
using namespace std;
inline int read(){
int x=0;char ch=' ';int f=1;
while(ch!='-'&&(ch<'0'||ch>'9'))ch=getchar();
if(ch=='-')f=-1,ch=getchar();
while(ch>='0'&&ch<='9')x=(x<<3)+(x<<1)+(ch^48),ch=getchar();
return x*f;
}
const int N=105,M=1005,p=31011;
struct edge{
int x,y,l;
inline bool operator < (const edge& b) const {
return l<b.l;
}
}e[M];
struct data{int l,r,v;}a[M];
int n,m,ans=1,cnt;
int fa
,sum;
inline int find(int x){return fa[x]==x?x:find(fa[x]);}
inline void dfs(int x,int now,int k){
if(now>a[x].r){
if(k==a[x].v)sum++;
return;
}
int u=find(e[now].x),v=find(e[now].y);
if(u!=v){
fa[u]=v;
dfs(x,now+1,k+1);
fa[u]=u;fa[v]=v;
}
dfs(x,now+1,k);
}
int main(){
n=read();m=read();
for(int i=1;i<=n;i++)fa[i]=i;
for(int i=1;i<=m;i++)e[i].x=read(),e[i].y=read(),e[i].l=read();
sort(e+1,e+m+1);int tot=0;
for(int i=1;i<=m;i++){
if(e[i].l!=e[i-1].l)a[cnt].r=i-1,a[++cnt].l=i;
int u=find(e[i].x),v=find(e[i].y);
if(u==v)continue;
fa[u]=v;a[cnt].v++;tot++;
}
a[cnt].r=m;
if(tot!=n-1){printf("0");return 0;}
for(int i=1;i<=n;i++)fa[i]=i;
for(int i=1;i<=cnt;i++){
sum=0;
dfs(i,a[i].l,0);
ans=(ans*sum)%p;
for(int j=a[i].l;j<=a[i].r;j++){
int u=find(e[j].x),v=find(e[j].y);
if(u!=v)fa[u]=v;
}
}
printf("%d",ans);
return 0;
}