【HDOJ】1109 Run Away

基础模拟退火。

 /* poj 1379 */
 #include <iostream>
 #include <cstdio>
 #include <cstdlib>
 #include <cstring>
 #include <cmath>
 #include <algorithm>
 using namespace std;

 #define MAXN 1005
 #define INF     999999
 #define MAXM 25

 typedef struct {
     double x, y;
 } Point_t;

 const double eps = 1e-;
 const double next = 0.9;
 const double PI = acos(-1.0);
 double X, Y;
 int n;
 Point_t points[MAXN];
 Point_t rpoints[MAXM];
 double rdis[MAXM];

 inline bool check(Point_t p) {
     return p.x< || p.x>=X || p.y< || p.y>=Y;
 }

 double cross(Point_t a, Point_t b, Point_t c) {
     return (b.x-a.x)*(c.y-a.y) - (c.x-a.x)*(b.y-a.y);
 }

 double Length(Point_t a, Point_t b) {
     return sqrt((a.x-b.x)*(a.x-b.x) + (a.y-b.y)*(a.y-b.y));
 }

 double solve(Point_t p) {
     int i, j, k;
     double ret = INF;

     for (i=; i<n; ++i) {
         ret = min(ret, Length(p, points[i]));
     }

     return ret;
 }

 int main() {
     int t;
     int i, j, k;
     Point_t p, pp;
     double step, angle;
     double ans, tmp;

     #ifndef ONLINE_JUDGE
         freopen("data.in", "r", stdin);
     #endif

     scanf("%d", &t);
     while (t--) {
         scanf("%lf %lf %d", &X, &Y, &n);
         for (i=; i<n; ++i)
             scanf("%lf %lf", &points[i].x, &points[i].y);
         for (i=; i<MAXM; ++i) {
             rpoints[i].x = (rand()%+)/1000.0*X;
             rpoints[i].y = (rand()%+)/1000.0*Y;
             rdis[i] = solve(rpoints[i]);
         }
         step = max(X, Y)/sqrt(1.0*n);
         while (step > eps) {
             for (i=; i<MAXM; ++i) {
                 p = rpoints[i];
                 for (j=; j<MAXM; ++j) {
                     angle = (rand()%+)/.**PI;
                     pp.x = p.x + cos(angle)*step;
                     pp.y = p.y + sin(angle)*step;
                     if (check(pp))
                         continue;
                     tmp = solve(pp);
                     if (tmp > rdis[i]) {
                         rpoints[i] = pp;
                         rdis[i] = tmp;
                     }
                 }
             }
             step *= next;
         }
         double ans = -1.0;
         k = ;
         for (i=; i<MAXM; ++i) {
             if (rdis[i] > ans) {
                 ans = rdis[i];
                 k = i;
             }
         }
         printf("The safest point is (%.1lf, %.1lf).\n", rpoints[k].x, rpoints[k].y);
     }

     return ;
 }