BZOJ4237 稻草人

#include <iostream>
#include <iomanip>
#include <cstdlib>
#include <cstdio>
#include <cmath>
#include <algorithm>
#include <string>
#include <cstring>
#define File(a) freopen(a".in","r",stdin),freopen(a".out","w",stdout)
#define RG register
#define ll long long
const int N = 200500;

using namespace std;

int gi(){char ch=getchar();int x=0;
    while(ch<‘0‘ || ch>‘9‘)ch=getchar();
    while (ch>=‘0‘ && ch<=‘9‘) {x=x*10+ch-‘0‘;ch=getchar();}
    return x;}
int n;ll ans;
struct date{int x,y;}f[N],a1[N],a2[N],q1[N],q2[N];
int cmp(date a,date b){return a.x<b.x;}
int cop(date a,date b){return a.y<b.y;}
int find(int h,int x){
    int l=1,r=x,k=0,mid;
    while(l<=r){
        mid=(l+r)>>1;
        if (q2[mid].y<h) r=mid-1;
        else l=mid+1,k=mid;
    }
    return k;
}

void cdq(int l,int r){
    if (l>=r) return;
    int mid=(l+r)>>1,b1=0,b2=0,top1=0,top2=0;RG int i,j,t=0;
    q1[0]=(date){n+1,n+1};
    cdq(l,mid);
    cdq(mid+1,r);
    for (i=l,j=mid+1; i<=mid; i++){
        a1[++b1]=f[i];
        while(j<=r && f[j].y>f[i].y){
            a2[++b2]=f[j];
            while(top2 && f[j].x<q2[top2].x) top2--;
            q2[++top2]=f[j++];
        }
        while(top1 && f[i].x>q1[top1].x) top1--;
        q1[++top1]=f[i];
        ans+=top2-find(q1[top1-1].y,top2);
    }
    while(j<=r) a2[++b2]=f[j++];
    i=1,j=1,t=l;
    while(i<=b1 && j<=b2)
        if (a1[i].y>a2[j].y) f[t++]=a1[i++];
        else f[t++]=a2[j++];
     while(i<=b1) f[t++]=a1[i++];
    while(j<=b2) f[t++]=a2[j++];
    return;
}

int main(){
    File("4237");
    RG int i;n=gi();
    for (i=1; i<=n; i++) f[i]=(date){gi()+1,gi()+1};
    sort(f+1,f+n+1,cop);
    for (i=1; i<=n; i++) f[i].y=i;
    sort(f+1,f+n+1,cmp);
    for (i=1; i<=n; i++) f[i].x=i;
    cdq(1,n);
    printf("%lld",ans);
    return 0;
}