2783: [JLOI2012]树

#include<iostream>
#include<cstdio>
#include<cstring>
#include<set>
using namespace std;
const int N=100000+5;
multiset<int>s;
struct Edge{int to,next;}e[N*2];
int head
,cnt,v
,S,sum
,ans;
void ins(int u,int v){
e[++cnt].to=v;e[cnt].next=head[u];head[u]=cnt;
}
void dfs(int u){
if(s.find(sum[u]-S)!=s.end())ans++;
s.insert(sum[u]);
for(int i=head[u];i;i=e[i].next){
sum[e[i].to]=sum[u]+v[e[i].to];
dfs(e[i].to);
}
s.erase(s.find(sum[u]));
}
int main(){
int n;scanf("%d%d",&n,&S);
s.insert(0);
for(int i=1;i<=n;i++)scanf("%d",&v[i]);
int from,to;
for(int i=1;i<n;i++){
scanf("%d%d",&from,&to);
ins(from,to);
}sum[1]=v[1];
dfs(1);
printf("%d",ans);
return 0;
}