poj 1389 Area of Simple Polygons

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
using namespace std;
#define N 11000
struct node1{
int x,y1,y2;
int flag;
}a
;
struct node2{
int down,up,x;
int cover,child;
}anode
;
int y
,yd
;
int m,n;
int cmp(node1 a,node1 b){
return a.x<b.x;
}
void bulid(int l,int r,int n){
anode
.down=yd[l];
anode
.up=yd[r];
anode
.child=1;
anode
.cover=0;
if(l==r-1){
anode
.child=0;
return;
}
int mid=(l+r)>>1;
bulid(l,mid,2*n);
bulid(mid,r,2*n+1);
}
int update(int l,int r,int x,int flag,int n){
if(anode
.up <= l || anode
.down >= r)
return 0;
if(anode
.child == 0)
{
if(anode
.cover > 0)
{
int ans = (x-anode
.x)*(anode
.up-anode
.down);
anode
.cover += flag;
anode
.x = x;
return ans;
}
else
{
anode
.cover += flag;
anode
.x = x;
return 0;
}
}
return update(l,r,x,flag,2*n)+update(l,r,x,flag,2*n+1);
}
int    main(){
int i,j,t=1;
int x1,y1,x2,y2,aera;
while(1){
m=0;
while(scanf("%d %d %d %d",&x1,&y1,&x2,&y2)){
if(x1==-1&&y1==-1&&x2==-1&&y2==-1){
if(m!=0)
break;
else{
t=0;
break;
}
}
m++;
a[m].x=x1,a[m].y1=y1,a[m].y2=y2,a[m].flag=1;
y[m]=y1;
m++;
a[m].x=x2,a[m].y1=y1,a[m].y2=y2,a[m].flag=-1;
y[m]=y2;
}
if(!t)
break;
sort(y+1,y+1+m);
sort(a+1,a+1+m,cmp);
j=1;
yd[1]=y[1];
for(i=2;i<=m;i++){
if(y[i]!=y[i-1])
yd[++j]=y[i];
}
bulid(1,j,1);
aera=0;
for(i=1;i<=m;i++)
aera+=update(a[i].y1,a[i].y2,a[i].x,a[i].flag,1);
printf("%d\n",aera);
}
return 0;
}