682C - Alyona and the Tree - CodeForces Solution

#include<cstdio>
const int N=1e5+1;
bool f[N];
int i,j,k,n,t,a[N],sz[N];
int fa[N],en[N],nxt[N],w[N];
void dfs(int u,long long d)
{
if(d>a[u])return;
if(d<0)d=0;
for(int i=fa[u];i;i=nxt[i])
dfs(en[i],d+w[i]);
f[u]=1;
}
int main()
{
scanf("%d",&n);
for(i=1;i<=n;++i)
scanf("%d",a+i);
for(i=2;i<=n;w[i++]=t)
{
scanf("%d%d",&j,&t);
en[i]=i,nxt[i]=fa[j],fa[j]=i;
}
for(dfs(i=1,j=0);i<=n;++i)j+=f[i];
printf("%d",n-j);
}