POJ2069 最小球体覆盖, 模拟退火

 1 //#pragma comment(linker, "/STACK:16777216") //for c++ Compiler
 2 #include <stdio.h>
 3 #include <iostream>
 4 #include <cstring>
 5 #include <cmath>
 6 #include <stack>
 7 #include <queue>
 8 #include <vector>
 9 #include <algorithm>
10 #define ll long long
11 #define Max(a,b) (((a) > (b)) ? (a) : (b))
12 #define Min(a,b) (((a) < (b)) ? (a) : (b))
13 #define Abs(x) (((x) > 0) ? (x) : (-(x)))
14 using namespace std;
15 
16 const int INF = 0x3f3f3f3f;
17 const int MAXN = 220;
18 const double eps = 1e-8;
19 int n;
20 struct POINT{
21     double x,y,z;
22 }ps[35],q;
23 
24 double dist(POINT a,POINT b){
25     return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y)+(a.z-b.z)*(a.z-b.z));
26 }
27 
28 int maxD(POINT p){
29     double res = 0;
30     int i, k = 0;
31     for(i = 0; i < n ; ++i){
32         double tmp = dist(p,ps[i]);
33         if(tmp > res){
34             k = i;
35             res = dist(p,ps[i]);
36         }
37     }
38     return k;
39 }
40 
41 double BallCover(){
42     double step = 100, ans = INF;
43     q.x = q.y = q.z = 0.0;
44     while(step > eps){
45         int d = maxD(q);
46         double tmp = dist(ps[d],q);
47         if(tmp < ans) ans=tmp;
48         double dx = ps[d].x - q.x;
49         double dy = ps[d].y - q.y;
50         double dz = ps[d].z - q.z;
51         dx /= tmp;
52         dy /= tmp;
53         dz /= tmp;
54         q.x += (dx*step);
55         q.y += (dy*step);
56         q.z += (dz*step);
57         step *= 0.98;
58     }
59     return ans;
60 }
61 
62 int main(){
63     int i;
64     while(EOF != scanf("%d",&n)){
65         if(0 == n)  break;
66         for(i = 0; i < n ; ++i)
67             scanf("%lf%lf%lf",&ps[i].x,&ps[i].y,&ps[i].z);
68         printf("%.5f\n",BallCover());
69     }
70     return 0;
71 }