Weak Pair HDU

Weak Pair HDU - 5877 T14 D57

思路：

dfs过程中遇见节点就将节点保存起来，此节点递归完成后将此节点删除，树状数组保存。

注意1不一定是根节点。

参考代码

#include<bits/stdc++.h>
#define ll long long
#define pb push_back
#define si size()
using namespace std;
ll read(){ll x=0,f=1;char ch=getchar();while(ch<'0'||ch>'9'){if(ch=='-') f=-1;ch=getchar();}while(ch>='0'&&ch<='9'){x=(x<<1)+(x<<3)+(ch^48);ch=getchar();}return x*f;}
inline void Prin(ll x){if(x < 0){putchar('-');x = -x;}if(x > 9) Prin(x / 10);putchar(x % 10 + '0');}
const int qs=1e5+7;
ll T,n,m,k,ans,a[qs],ct,b[qs],c[qs],u[qs];
vector<int> v[qs];

int lowbit(int x){return (x&(-x));};
ll get(int x){	return lower_bound(b+1,b+1+ct,x)-b;}
void add(int x,int y){for(;x<=ct;x+=lowbit(x)) c[x]+=y;}
ll ask(int x){ll as=0;for(;x;x-=lowbit(x)) as+=c[x];return as;}

void dfs(int x,int fa){
	int f=upper_bound(b+1,b+1+ct,k/a[x])-b-1;
	ans=ans+ask(f);
	add(get(a[x]),1);
	for(int i=0;i<v[x].si;++i){
		int p=v[x][i];
		if(p==fa) continue;
		dfs(p,x);
	}
	add(get(a[x]),-1);
}

int main(){
	
	T=read();
	while(T--){
		n=read(),k=read();
		ans=0;
		int x,y;
		
		for(int i=0;i<=n;++i) v[i].clear(),c[i]=u[i]=0;
		for(int i=1;i<=n;++i) a[i]=read(),b[i]=a[i];
		sort(b+1,b+1+n);
		ct=unique(b+1,b+1+n)-b-1;
		for(int i=1;i<n;++i){
			x=read(),y=read();
			v[x].pb(y);
			u[y]++;
		}
		int id;
        for(int i=1;i<=n;++i) if(!u[i]) id=i;
		dfs(id,0);
		cout<<ans<<"
";
	}
	return 0;
}