luogu P2344 [USACO11FEB]Generic Cow Protests G

题面传送门
考虑暴力\(dp\):设\(dp_i\)表示以\(i\)结尾的分组方案数，\(q_i=\sum\limits_{j=1}^{i}a_i\)
那么\(dp_i=\sum\limits_{j=1}^{i-1}{dp_j[q_i-q_j\geq0]}+[q_i\geq0]\)
然后发现这个是一个二维偏序板子。就可以树状数组优化了。
代码实现:

#include<cstdio>
#include<algorithm>
#define mod 1000000009
using namespace std;
int a[100039],q[100039],n,m,k,x,y,z,l,r,mid,nows[100039],tots[100039];
long long f[100039],dp[100039];
inline void get(int x,int y){while(x<=n)f[x]+=y,x+=x&-x;}
inline long long find(int x){long long ans=0;while(x)ans+=f[x],x-=x&-x;return ans;}
int main(){
	register int i;
	scanf("%d",&n);
	for(i=1;i<=n;i++) scanf("%d",&a[i]),q[i]=q[i-1]+a[i],nows[i]=q[i];
	sort(nows+1,nows+n+1);
	nows[0]=nows[1]-1;
	for(i=1;i<=n;i++){
		tots[i]=tots[i-1];
		if(nows[i]!=nows[i-1]) tots[i]++;
	}
	for(i=1;i<=n;i++){
		if(q[i]>=0) dp[i]=1; 
		l=0;r=n+1;
		while(l+1<r){
			mid=(l+r)>>1;
			if(nows[mid]<q[i]) l=mid;
			else r=mid;
		}
		q[i]=tots[r];
	}
	for(i=1;i<=n;i++){
		dp[i]+=find(q[i])%mod;
		get(q[i],dp[i]);
	}
	printf("%lld\n",dp[n]);
}