bzoj 1007: [HNOI2008]水平可见直线

 1 #include<cstdio>
 2 #include<iostream>
 3 #include<algorithm>
 4 #define M 1000000
 5 using namespace std;
 6 struct data
 7 {
 8     int k,b,nu;
 9 }a[M];
10 int n,q[M],t;
11 bool cmp(data a1,data a2)
12 {
13     if(a1.k==a2.k)
14       return a1.b<a2.b;
15     return a1.k<a2.k;
16 }
17 bool cmp1(int a1,int a2)
18 {
19     return a[a1].nu<a[a2].nu;
20 }
21 double crossx(data x1,data x2)
22 {   
23     double s1=(x2.b-x1.b),s2=(x1.k-x2.k);
24     return s1/s2;
25 }
26 bool pan(int a1)
27 {
28     if(a[a1].k==a[q[t]].k)
29       return 1;
30     if(t>1&&crossx(a[a1],a[q[t-1]])<=crossx(a[q[t]],a[q[t-1]]))
31       return 1;
32     return 0; 
33 }
34 int main()
35 {
36     scanf("%d",&n);
37     for(int i=1;i<=n;i++)
38       {
39         scanf("%d%d",&a[i].k,&a[i].b);
40         a[i].nu=i;
41       }
42     sort(a+1,a+n+1,cmp);
43     q[1]=1;
44     t=1;
45     for(int i=2;i<=n;i++)
46       {
47         for(;t&&pan(i);t--);
48         q[++t]=i;
49       }
50     sort(q+1,q+t+1,cmp1);
51     for(int i=1;i<=t;i++)
52       printf("%d ",a[q[i]].nu);
53     return 0;
54 }