POJ 1379 （随机算法）模拟退火

题目大意：

给定一堆点，找到一个点的位置使这个点到所有点中的最小距离最大

这里数据范围很小，精度要求也不高，我们这里可以利用模拟退火的方法，随机找到下一个点，如果下一个点比当前点优秀就更新当前点

参考：http://www.cnblogs.com/heaad/archive/2010/12/20/1911614.html

http://wenku.baidu.com/view/0c6b5df5f61fb7360b4c65a9.html

 #include <cstdio>
 #include <cstring>
 #include <iostream>
 #include <algorithm>
 #include <climits>
 #include <cmath>
 #include <queue>
 #include <cstdlib>
 #include <ctime>
 using namespace std;
 #define random(x) ((rand()%x)+1)
 #define N 1005
 #define ll long long
 #define eps 1e-4
 const double PI = acos(-1.0);
 const int INF = INT_MAX;
 const int P = ;
 const int L = ;

 double x,y;
 int n;
 double dist[N];

 struct Point{
     double x,y;
     Point(double x= , double y=):x(x),y(y){}
 }p[N] , tmp[N];

 double dis(Point a , Point b)
 {
     double x = a.x-b.x , y = a.y - b.y;
     return sqrt(x*x+y*y);
 }

 double min_dis(Point t)
 {
     double minn = 1e20;
     for(int i= ; i<n ; i++) minn=min(minn , dis(t , p[i]));
     return minn;
 }

 bool ok(Point t)
 {
     return t.x>= && t.x<=x && t.y>= && t.y<=y;
 }

 int main()
 {
     #ifndef ONLINE_JUDGE
         freopen("a.in" , "r" , stdin);
     #endif // ONLINE_JUDGE
     srand(time());
     int T;
     scanf("%d" , &T);
     while(T--)
     {
         Point ans;
         double ret=;

         scanf("%lf%lf%d" , &x , &y , &n);
         for(int i= ; i<n ; i++){
             scanf("%lf%lf" , &p[i].x , &p[i].y);
         }

         for(int i= ; i<P ; i++){
             tmp[i].x = random()/1000.0*x;
             tmp[i].y = random()/1000.0*y;
             dist[i] = min_dis(tmp[i]);
         }
         double step = sqrt(x*x+y*y)/;
         while(step>eps){

             for(int i= ; i<P ; i++){
                 Point cur;
                 for(int j= ; j<L ; j++){
                     double ang = random()/1000.0**PI;
                     cur.x = tmp[i].x+cos(ang)*step;
                     cur.y = tmp[i].y+sin(ang)*step;
                     if(!ok(cur)) continue;
                     double val = min_dis(cur);
                     if(val>dist[i]){
                         tmp[i]=cur;
                         dist[i] = val;
                     }
                 }
             }
             step *= 0.85;
         }

         for(int i= ; i<P ; i++){
             if(dist[i]>ret){
                 ret = dist[i];
                 ans = tmp[i];
             }
         }
         printf("The safest point is (%.1f, %.1f).\n" , ans.x , ans.y);
     }
     return ;
 }