spoj mpoint

题解：

判断每一次加进来的时候有几个被破坏，几个添加

然后单调栈维护

代码：

#include<bits/stdc++.h>
using namespace std;
const int N=5005;
int n,j,k,ans=0,now,oo=10000000;
struct note{int x,y,id;}a[N],b[N];
bool cmp(const note i,const note j){return i.x<j.x;}
struct stack
{
    note e[N]; int l,h,t;
    void pre(int z){l=0;h=t=0;e[0].x=now;e[0].y=oo*z;}
    void add(note a,bool z){if ((a.y<e[l].y)^z)e[++l]=a;}
    void Xwork(int x,bool z){while (h<=l&&((e[h].x<x)^z))h++;h?h--:0;}
    void Ywork(int y,bool z){while (t<=l&&((e[t].y<y)^z))t++;}
}c1,c2,c3,c4;
int main()
{
    scanf("%d",&n);
    for (int i=1;i<=n;i++)scanf("%d%d",&a[i].x,&a[i].y),a[i].id=i;
    memcpy(b,a,sizeof(b));
    std::sort(b+1,b+n+1,cmp);
    for (int i=1;i<=n;i++)
     {
        now=a[i].x;c1.pre(1),c2.pre(1);c3.pre(-1),c4.pre(-1);
        for (k=1;k<=n&&b[k].x<a[i].x;k++);
        for (j=k-1;j;j--)
         if (b[j].id<i)
          if (b[j].y>a[i].y) c2.add(b[j],0); 
          else c3.add(b[j],1);
        for (j=k;j<=n;j++) 
         if (b[j].id<i)
          if (b[j].y>a[i].y) c1.add(b[j],0); 
          else c4.add(b[j],1);
        ans+=c1.l+c2.l+c3.l+c4.l;
        for (int j=1;j<=c1.l;j++)
         {
            int x=c1.e[j].x,y=c1.e[j].y,xx,yy; 
            if (!c3.l) continue;
            c2.Ywork(y,1);xx=c2.e[c2.t].x; 
            if (c2.t>c2.l) xx=-oo;c3.Xwork(xx,1);
            c4.Xwork(x,0);yy=c4.e[c4.h].y;c3.Ywork(yy,0);
            c3.h>c3.l?c3.h--:0;c3.t?0:c3.t++;
            ans-=max(c3.h-c3.t+1,0);
         }
        c2.h=c2.t=c3.h=c3.t=c4.h=c4.t=1;
        for (int j=1;j<=c4.l;j++)
         {
            int x=c4.e[j].x,y=c4.e[j].y,xx,yy; 
            if (!c2.l) continue;
            c3.Ywork(y,0);xx=c3.e[c3.t].x;
             if (c3.t>c3.l) xx=-oo;c2.Xwork(xx,1);
            c1.Xwork(x,0);yy=c1.e[c1.h].y;c2.Ywork(yy,1);
            c2.h>c2.l?c2.h--:0;c2.t?0:c2.t++;ans-=max(c2.h-c2.t+1,0);
         }
        printf("%d\n",ans);
     }
    return 0;
}