POJ3714 Raid 平面最近点对

利用分治来求平面最近点对

只需要查后面6个点就好了

原因在于https://blog.csdn.net/liufeng_king/article/details/8484284

两个集合的话就把不同集合的设为inf就好了

 1 const db inf = 1e100;
 2 
 3 ll sqr(ll x) { return x*x; }
 4 
 5 struct point {
 6     int x,y;
 7     int f;
 8     void in() {
 9         scanf("%d%d",&x,&y);
10     }
11     point operator-(const point &b) const {
12         point ret;
13         ret.x=x-b.x;
14         ret.y=y-b.y;
15         return ret;
16     }
17     db mean() {
18         ll ret=0;
19         ret=sqr(x)+sqr(y);
20         return sqrt(ret);
21     }
22 };
23 
24 point a[N];
25 
26 db dis(point a,point b) {
27     db ret=0;
28     if(a.f==b.f) return inf;
29     ret=(a-b).mean();
30     return ret;
31 }
32 
33 bool cmp_x(point a,point b) {
34     return a.x<b.x;
35 }
36 
37 int t[N];
38 bool cmp_t(int x,int y) {
39     return a[t[x]].y<a[t[y]].y;
40 }
41 
42 db F(int l,int r) {
43     if(l==r) return inf;
44     if(l+1==r) return dis(a[r],a[l]);
45     int mid=(l+r)>>1;
46     db ans1=F(l,mid);
47     db ans2=F(mid+1,r);
48     db ans=min(ans1,ans2);
49     if(ans==0) return ans;
50     int nm=0;
51     for(int i=l;i<=r;i++) if(a[mid].x-ans<=a[i].x && a[i].x<=a[mid].x+ans) {
52         t[++nm]=i;
53     }
54     sort(t+1,t+nm+1,cmp_t);
55     for(int i=1;i<=nm;i++) {
56         for(int j=i+1;j<=min(nm,i+6);j++) {
57             db anss=dis(a[t[i]],a[t[j]]);
58             ans=min(ans,anss);
59         }
60     }
61     return ans;
62 }
63 
64 int main() {
65     int T;
66     scanf("%d",&T);
67     while(T--) {
68         int n;
69         scanf("%d",&n);
70         for(int i=1;i<=n;i++) {
71             a[i].in();
72             a[i].f=1;
73         }
74         for(int i=n+1;i<=2*n;i++) {
75             a[i].in();
76             a[i].f=2;
77         }
78         sort(a+1,a+2*n+1,cmp_x);
79         db ans=F(1,2*n);
80         printf("%.3f\n",ans);
81     }
82     return 0;
83 }

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