分治算法初步

 1 #include<cstdio>
 2 #include<cstring>
 3 #include<algorithm>
 4 #include<cstdlib>
 5 #include<cmath>
 6 #include<iostream>
 7 #define inf 0x3f3f3f3f
 8 using namespace std;
 9 typedef long long ll;
10 struct point{
11     double x,y;
12 }p[100002],tmp[100002];
13 double dis(point &a,point &b){
14     return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
15 }
16 bool cmp1(point &a,point &b){
17     return a.x<b.x;
18 }
19 bool cmp2(point &a,point &b){
20     return a.y<b.y;
21 }
22 double closet(int l,int r){
23     if(l==r) return inf;
24     if(l+1==r) return dis(p[l],p[r]);
25     int mid=(l+r)>>1;
26     double d1,d2,d;
27     d1=closet(l, mid),d2=closet(mid+1, r);
28     d=min(d1,d2);
29     int k=0;
30     for(int i=l;i<=r;i++){
31         if(fabs(p[i].x-p[mid].x)<mid) tmp[k++]=p[i];
32     }
33     sort(tmp, tmp+k,cmp2);
34     for(int i=0;i<k-1;i++){
35         for(int j=i+1;j<k;j++){
36             if(fabs(tmp[j].y-tmp[i].y)>=d) break;
37             d=min(d,dis(tmp[i],tmp[j]));
38         }
39     }
40     return d;
41 }
42 
43 
44 int main(){
45     int n;
46     while(scanf("%d",&n)!=EOF){
47         if(!n) continue;
48         for(int i=0;i<n;i++){
49             scanf("%lf%lf",&p[i].x,&p[i].y);
50         }
51         sort(p,p+n,cmp1);
52         double ans=closet(0, n-1);
53         printf("%.2f\n",ans/2);
54     }
55     
56 }