扫描线概览

poj 1151:

可以说是计算几何的扫描线入门题吧。挺简单的，线段树建树部分要想想。其他就看码力了。

  1 //13435314    ooyyloo    1151    Accepted    748K    0MS    G++    2079B    2014-09-12 16:16:35
  2 #include <cstdio>
  3 #include <algorithm>
  4 #include <iostream>
  5 #include <set>
  6 #define mp make_pair
  7 #define dbg(x) cout<<#x<<"="<<x<<endl
  8 #define foreach(it,v) for(__typeof(v.begin()) it=v.begin();it!=v.end();it++)
  9 using namespace std;
 10 const int maxn=201;
 11
 12 struct line{
 13     double x,y1,y2;
 14     int v;
 15     bool operator< (const line &a) const { return x<a.x; }
 16 }wu[maxn];
 17
 18 int n,nn;
 19 double ans;
 20 set<double> sety;
 21 double hashy[maxn]; int hpo;
 22
 23 //seg tree
 24 double sh[maxn<<2]; int cov[maxn<<2];
 25 void build(int k,int l,int r)
 26 {
 27     sh[k]=cov[k]=0;
 28     if (l+1==r) return;
 29     int mid=l+r>>1;
 30     build(k<<1,l,mid);
 31     build(k<<1|1,mid,r);
 32 }
 33 void update(int k,int l,int r)
 34 {
 35     if (cov[k])      sh[k]=hashy[r]-hashy[l];
 36     else if (l+1==r) sh[k]=cov[k]?hashy[r]-hashy[l]:0;
 37     else              sh[k]=sh[k<<1]+sh[k<<1|1];
 38 }
 39 void modify(int k,int l,int r,int ll,int rr,int v)//we just care about father
 40 {
 41     if (l>=ll&&r<=rr)
 42     {
 43         cov[k]+=v;
 44         update(k,l,r);
 45         return;
 46     }
 47     int mid=l+r>>1;
 48     if (ll<mid) modify(k<<1,l,mid,ll,rr,v);
 49     if (rr>mid) modify(k<<1|1,mid,r,ll,rr,v);
 50     update(k,l,r);
 51 }
 52
 53
 54 void init()
 55 {
 56     nn=n<<1;
 57     sety.clear();
 58
 59     double x1,y1,x2,y2;
 60     for (int i=1;i<=n;i++)
 61     {
 62         scanf("%lf%lf%lf%lf",&x1,&y1,&x2,&y2);
 63         wu[i].x=x1; wu[i].y1=y1; wu[i].y2=y2; wu[i].v=1;
 64         wu[i+n].x=x2; wu[i+n].y1=y1; wu[i+n].y2=y2; wu[i+n].v=-1;
 65         sety.insert(y1); sety.insert(y2);
 66     }
 67     hpo=0;
 68     foreach(it,sety) hashy[++hpo]=*it;
 69     //for (auto x:sety) hashy[++hpo]=x;
 70 }
 71 int bs(double d)
 72 {
 73     int l=1,r=hpo,mid;
 74     while (l<=r)
 75     {
 76         mid=l+r>>1;
 77         if (d>hashy[mid]) l=mid+1;
 78         else               r=mid-1;
 79     }
 80     return l;
 81 }
 82 void solve()
 83 {
 84     ans=0.0;
 85     sort(wu+1,wu+1+nn);
 86     modify(1,1,hpo,bs(wu[1].y1),bs(wu[1].y2),wu[1].v);
 87     for (int z=2;z<=nn;z++)
 88     {
 89         ans+=sh[1]*(wu[z].x-wu[z-1].x);
 90         modify(1,1,hpo,bs(wu[z].y1),bs(wu[z].y2),wu[z].v);
 91     }
 92 }
 93 int main()
 94 {
 95     for (int tt=1;scanf("%d",&n)!=EOF;tt++)
 96     {
 97         if (!n) break;
 98         init();
 99         build(1,1,hpo);
100         solve();
101         printf("Test case #%d\n",tt);
102         printf("Total explored area: %.2f\n",ans);
103         puts("");
104     }
105     return 0;
106 }

//scanning line 1