LUOGU P2344 奶牛抗议 (树状数组优化dp)

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cstdlib>

using namespace std;
const int MAXN = 100005;
const int mod = 1000000009;

inline int rd(){
    int x=0,f=1;char ch=getchar();
    while(!isdigit(ch)) {f=ch==‘-‘?0:1;ch=getchar();}
    while(isdigit(ch))  {x=(x<<1)+(x<<3)+ch-‘0‘;ch=getchar();}
    return f?x:-x;
}

//f[i] 到了第i个人
//f[i]=f[i-k]+1 

int f[MAXN],t[MAXN],rk[MAXN];
int n,sum[MAXN],cpy[MAXN];

inline bool cmp(int x,int y){
    return x<y;
}

int query(int x){
    int ret=0;
    for(;x;x-=x&-x) ret+=t[x],ret%=mod;
    return ret;
}

void update(int x,int k){
    for(;x<=n;x+=x&-x) t[x]+=k,t[x]%=mod;
}

int main(){
    n=rd();f[0]=1;
    for(register int i=1;i<=n;i++) sum[i]=sum[i-1]+rd(),cpy[i]=sum[i];
    sort(cpy+1,cpy+1+n,cmp);int u=unique(cpy+1,cpy+1+n)-cpy-1;
    for(register int i=1;i<=n;i++) rk[i]=lower_bound(cpy+1,cpy+1+u,sum[i])-cpy;
    for(register int i=1;i<=n;i++){
        if(sum[i]>=0) f[i]=1;
        f[i]+=query(rk[i]);
        update(rk[i],f[i]);
    }
    cout<<f[n]<<endl;
    return 0;
}