hdu 1255 覆盖的面积

http://acm.hdu.edu.cn/showproblem.php?pid=1255

 #include <cstdio>
 #include <cstring>
 #include <algorithm>
 #define maxn 100010
 using namespace std;

 int t,n;
 double Y[maxn],X[maxn];
 struct point
 {
     double x;
     double y_up;
     double y_down;
     int lr;
     bool operator <(const point &a) const
     {
         return x<a.x;
     }
 }p[maxn*];

 struct node
 {
     double x;
     double y_up;
     double y_down;
     int cover;
     bool flag;
 }tree[maxn*];

 void build(int i,int l,int r)
 {
     tree[i].x=-;
     tree[i].y_up=Y[r];
     tree[i].y_down=Y[l];
     tree[i].cover=;
     tree[i].flag=true;
     if(l+==r)
     {
         tree[i].flag=false;
         return ;
     }
     int mid=(l+r)>>;
     build(i<<,l,mid);
     build(i<<|,mid,r);
 }

 double update(int i,double l,double r,double x,int lr)
 {
     if(tree[i].y_down>=r||tree[i].y_up<=l) return ;
     if(!tree[i].flag)
     {
         if(tree[i].cover>)
         {
             tree[i].cover+=lr;
             double sum=(x-tree[i].x)*(tree[i].y_up-tree[i].y_down);
             tree[i].x=x;
             return sum;
         }
         else
         {
             tree[i].cover+=lr;
             tree[i].x=x;
             return ;
         }
     }
     else return update(i<<,l,r,x,lr)+update(i<<|,l,r,x,lr);
 }
 int main()
 {
     scanf("%d",&t);
     while(t--)
     {
         scanf("%d",&n);
         int cnt=;
         for(int i=; i<=n; i++)
         {
             double x1,y1,x2,y2;
             scanf("%lf%lf%lf%lf",&x1,&y1,&x2,&y2);
             p[cnt].x=x1;
             p[cnt].y_down=y1;
             p[cnt].y_up=y2;
             p[cnt].lr=;
             X[cnt]=x1;
             Y[cnt++]=y1;
             p[cnt].x=x2;
             p[cnt].y_down=y1;
             p[cnt].y_up=y2;
             X[cnt]=x2;
             p[cnt].lr=-;
             Y[cnt++]=y2;
         }
         sort(Y,Y+cnt);
         sort(X,X+cnt);
         sort(p,p+cnt);
         build(,,cnt-);
         double ans=;
         for(int i=; i<cnt; i++)
         {
             ans+=update(,p[i].y_down,p[i].y_up,p[i].x,p[i].lr);
         }
         printf("%.2lf\n",ans);
     }
     return ;
 }