JZYZOJ1535 [haoi2014]穿越封锁线

 1 #include<iostream>  
 2 #include<cstdio>  
 3 #include<cstring>  
 4 #include<algorithm>  
 5 #include<cmath>
 6 #include<queue>
 7 #define lc x*2
 8 #define rc x*2+1
 9 using namespace std;
10 const int maxn=110;
11 int n,x,y;
12 int a[maxn]={};
13 int b[maxn]={};
14 struct wtf{
15     double y;
16     bool f;
17 }e[maxn];
18 int tot=0;
19 bool mmp(wtf xx,wtf yy){
20     return xx.y<yy.y;
21 }
22 int main(){
23     scanf("%d",&n);
24     for(int i=1;i<=n;i++){
25         scanf("%d%d",&a[i],&b[i]);
26     }a[0]=a[n];b[0]=b[n];
27     scanf("%d%d",&x,&y);int x1,x2,y1,y2;
28     for(int i=1;i<=n;i++){
29         if(a[i]==x){
30             e[++tot].y=b[i];e[tot].f=0;
31             if((a[i-1]-a[i])*(a[i+1]-a[i])>0) e[tot].f=1;
32         }
33         if((a[i]-x)*(a[i-1]-x)<0){
34             if(a[i]>a[i-1]){x1=a[i-1],x2=a[i],y1=b[i-1],y2=b[i];}
35             else {x1=a[i],x2=a[i-1],y1=b[i],y2=b[i-1];}
36             e[++tot].y=double(y2-y1)/(x2-x1)*(x-x1)+y1;
37             e[tot].f=0;
38         }
39     }
40     sort(e+1,e+1+tot,mmp);
41     double cnt=0,z;int f=1;
42     if(e[1].f)f=0;
43     for(int i=2;i<=tot;i++){
44         if(f&&e[i].y>y){
45             if(y>e[i-1].y)z=y;
46             else z=e[i-1].y;
47             cnt+=e[i].y-z;
48         }
49         if(!e[i].f)f=f^1;
50         
51     }int ans=cnt;
52     printf("%d\n",ans);
53     return 0;
54 }