bzoj4237

题解：

cdq分治

二位变成一维

二分一下

代码：

#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
const int N=;
int n,Stack[N],top,Stack2[N],tail;
LL ans;
struct node{int x,y;}a[N];
bool cmpx(node q,node qq){return q.x<qq.x;}
bool cmpy(node q,node qq){return q.y<qq.y;}
void solve(int l,int r)
{
    if (l==r) return;
    sort(a+l,a+r+,cmpy);
    int mid=(l+r)>>;
    sort(a+l,a+mid+,cmpx);
    sort(a+mid+,a+r+,cmpx);
    top=tail=;
    int now=l,L,R,pos,mm,cp;
    for (int i=mid+;i<=r;i++)
     {
        while (top>&&a[Stack[top]].y>=a[i].y)top--;
        Stack[++top]=i;
        while (now<=mid&&a[now].x<a[i].x)
         {
            while (tail>&&a[Stack2[tail]].y<=a[now].y) tail--;
            Stack2[++tail]=now;
            now++;
         }
        L=;R=tail;pos=-;cp=a[Stack[top-]].x;
        while (L<=R)
         {
            mm=(L+R)>>;
            if (a[Stack2[mm]].x>cp) pos=mm,R=mm-;
            else L=mm+;
         }
        if (pos!=-) ans+=tail-pos+;
     }
    solve(l,mid);
    solve(mid+,r);
}
int main()
{
    scanf("%d",&n);
    for (int i=;i<=n;i++)scanf("%d%d",&a[i].x,&a[i].y);
    a[].x=a[].y=-;
    solve(,n);
    printf("%lld",ans);
    return ;
}