POJ 1389 Area of Simple Polygons | 扫描线

 1 #include<cstdio>
 2 #include<algorithm>
 3 #include<cstring>
 4 #define N 1010
 5 #define LEN 60010
 6 using namespace std;
 7 struct Edge
 8 {
 9     int l,r,h,f;
10     bool operator < (const Edge &a) const
11     {
12         if (h==a.h) return f<a.f;
13         return h<a.h;
14     }
15 }edge[N*2];
16 int cnt,s[4*LEN],cover[4*LEN],mx;
17 long long ans;
18 void insert(int i,int l,int r,int x,int y,int k)
19 {
20     if (y<l || x>r) return;
21     if (x<=l && y>=r)
22     {
23     cover[i]+=k;
24     if (cover[i]>0) s[i]=r-l+1;
25     else if (l==r) s[i]=0;
26     else s[i]=s[i*2]+s[i*2+1];
27     return;
28     }
29     int mid=(l+r)>>1;
30     insert(i*2,l,mid,x,y,k);
31     insert(i*2+1,mid+1,r,x,y,k);
32     if (cover[i]==0) s[i]=s[2*i]+s[2*i+1];
33     return;
34 }
35 Edge make(int a,int b,int c,int d)
36 {
37     Edge ret;
38     ret.l=a,ret.r=b,ret.h=c,ret.f=d;
39     return ret;
40 }
41 int main()
42 {
43     int a,b,c,d;
44     while (1)
45     {
46     cnt=ans=mx=0;
47     while (1)
48     {
49         scanf("%d%d%d%d",&a,&b,&c,&d);
50         mx=max(mx,c);
51         if (a==-1 && b==-1 && c==-1 && b==-1) break;
52         edge[++cnt]=make(a,c,b,1);
53         edge[++cnt]=make(a,c,d,-1);
54     }
55     if (cnt==0) break;
56     memset(cover,0,sizeof(cover));
57     memset(s,0,sizeof(s));
58     sort(edge+1,edge+1+cnt);
59     insert(1,0,mx,edge[1].l+1,edge[1].r,edge[1].f);
60     for (int i=2;i<=cnt;i++)
61         ans+=s[1]*(edge[i].h-edge[i-1].h),insert(1,0,mx,edge[i].l+1,edge[i].r,edge[i].f);
62     printf("%lld\n",ans);
63     }
64     return 0;
65 }