hdu 刷题记录

1007 最近点对问题，采用分治法策略搞定

 1 #include<iostream>
 2 #include<cmath>
 3 #include<algorithm>
 4 using namespace std;
 5 int n;
 6 struct node
 7 {
 8   double x;
 9   double y;
10 }p[100005];
11 int a[100005];
12 double cmpx(node a,node b)
13 {
14   return a.x<b.x;
15 }
16 double cmpy(int a,int b)
17 {
18   return p[a].y<p[b].y;
19 }
20 double min(double a,double b)
21 {
22   return a<b?a:b;
23 }
24 double dis(node a,node b)
25 {
26   return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
27 }
28 double find(int l,int r)
29 {
30      if(r==l+1)
31       return dis(p[l],p[r]);
32      if(l+2==r)
33       return min(dis(p[l],p[r]),min(dis(p[l],p[l+1]),dis(p[l+1],p[r])));
34      int mid=(l+r)>>1;
35      double ans=min(find(l,mid),find(mid+1,r));
36      int i,j,cnt=0;
37      for(i=l;i<=r;i++)
38      {
39        if(p[i].x>=p[mid].x-ans&&p[i].x<=p[mid].x+ans)
40           a[cnt++]=i;
41      }
42      sort(a,a+cnt,cmpy);
43      for(i=0;i<cnt;i++)
44      {
45        for(j=i+1;j<cnt;j++)
46        {
47          if(p[a[j]].y-p[a[i]].y>=ans) break;
48          ans=min(ans,dis(p[a[i]],p[a[j]]));
49        }
50      } 
51      return ans;
52 }
53 int main()
54 {
55     int i;
56    
57     while(scanf("%d",&n)!=EOF)
58     {
59       if(!n) break;
60       for(i=0;i<n;i++)
61        scanf("%lf %lf",&p[i].x,&p[i].y);
62       sort(p,p+n,cmpx);
63       printf("%.2lf%\n",find(0,n-1)/2);
64     }
65     return 0;
66 }

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