Luogu P1429 平面最近点对 【分治】By cellur925

 1 #include<cstdio>
 2 #include<algorithm>
 3 #include<cmath> 
 4 
 5 using namespace std;
 6 
 7 int n;
 8 int que[200090];
 9 struct node{
10     double x,y;
11 }p[200090];
12 bool cmp(node a,node b)
13 {
14     return a.x<b.x;
15 }
16 
17 bool cmp2(int a,int b)
18 {
19     return p[a].y<p[b].y;
20 }
21 
22 double dis(int i,int j)
23 {
24     return sqrt((p[i].x-p[j].x)*(p[i].x-p[j].x)+(p[i].y-p[j].y)*(p[i].y-p[j].y));
25 }
26 
27 double merge(int l,int r)
28 {
29     double dd=1e8;
30     if(l==r) return dd;
31     if(l+1==r) return dis(l,r);
32     int mid=(l+r)>>1;
33     double dl=merge(l,mid);
34     double dr=merge(mid+1,r);
35     dd=min(dl,dr);
36     
37     int pos=0;
38     for(int i=l;i<=r;i++)
39         if(fabs(p[mid].x-p[i].x)<dd) que[++pos]=i;
40     sort(que+1,que+1+pos,cmp2);
41     for(int i=1;i<=pos;i++)
42         for(int j=i+1;j<=pos;j++)
43         {
44             if(dis(que[i],que[j])>dd) break;
45             double ddd=dis(que[i],que[j]);
46             dd=min(dd,ddd);
47         }
48     return dd;    
49 }
50 
51 int main()
52 {
53     scanf("%d",&n);
54     for(int i=1;i<=n;i++) scanf("%lf%lf",&p[i].x,&p[i].y);
55     sort(p+1,p+1+n,cmp);
56     printf("%.4lf",merge(1,n));
57     return 0;
58 }