luogu_P5459 [BJOI2016]回转寿司

#include<iostream>
#include<cstdio>

#define ri register int
#define u long long

namespace opt {

    inline u in() {
        u x(0),f(1);
        char s(getchar());
        while(s<‘0‘||s>‘9‘) {
            if(s==‘-‘) f=-1;
            s=getchar();
        }
        while(s>=‘0‘&&s<=‘9‘) {
            x=(x<<1)+(x<<3)+s-‘0‘;
            s=getchar();
        }
        return x*f;
    }

}

using opt::in;

#define NN 100005

#include<algorithm>

namespace mainstay {

    u ans(0),N,a[NN],s[NN],L,R;

    u erf(const u &l,const u &r,const u &x,const u &k) {
        u _l(l),_r(r),_re(0),mid;
        if(k) {
            while(_l<=_r) {
                mid=(_l+_r)>>1;
                if(s[mid]>x) _r=mid-1;
                else _re=mid,_l=mid+1;
            }
            return _re;
        }
        while(_l<=_r) {
            mid=(_l+_r)>>1;
            if(s[mid]<x) _l=mid+1;
            else _re=mid,_r=mid-1;
        }
        return _re;
    }

    void dfs(const u &l,const u &r) {
        if(l==r) {
            s[l]=a[l]-a[l-1],ans+=(s[l]>=L&&s[l]<=R);
            return;
        }
        u mid((l+r)>>1);
        dfs(l,mid),dfs(mid+1,r);
        for(ri i(l); i<=mid; ++i) {
            u _x(a[mid]-a[i-1]),_y(L-_x),_z(R-_x);
            u _r(erf(mid+1,r,_z,1)),_l(erf(mid+1,r,_y,0));
            ans+=(_l&&_r)?(_r-_l+1):(0);
        }
        for(ri i(l); i<=r; ++i) s[i]=a[i]-a[l-1];
        std::sort(s+l,s+r+1);
    }

    inline void solve() {
        N=in(),L=in(),R=in();
        for(ri i(1); i<=N; ++i) a[i]=a[i-1]+in();
        dfs(1,N),std::cout<<ans;
    }

}

int main() {

    //freopen("4627.in","r",stdin);
    //freopen("4627.out","w",stdout);
    mainstay::solve();

}