【HDOJ】1109 Run Away

基础模拟退火。

  1 /* poj 1379 */
  2 #include <iostream>
  3 #include <cstdio>
  4 #include <cstdlib>
  5 #include <cstring>
  6 #include <cmath>
  7 #include <algorithm>
  8 using namespace std;
  9
 10 #define MAXN 1005
 11 #define INF     999999
 12 #define MAXM 25
 13
 14 typedef struct {
 15     double x, y;
 16 } Point_t;
 17
 18 const double eps = 1e-3;
 19 const double next = 0.9;
 20 const double PI = acos(-1.0);
 21 double X, Y;
 22 int n;
 23 Point_t points[MAXN];
 24 Point_t rpoints[MAXM];
 25 double rdis[MAXM];
 26
 27 inline bool check(Point_t p) {
 28     return p.x<0 || p.x>=X || p.y<0 || p.y>=Y;
 29 }
 30
 31 double cross(Point_t a, Point_t b, Point_t c) {
 32     return (b.x-a.x)*(c.y-a.y) - (c.x-a.x)*(b.y-a.y);
 33 }
 34
 35 double Length(Point_t a, Point_t b) {
 36     return sqrt((a.x-b.x)*(a.x-b.x) + (a.y-b.y)*(a.y-b.y));
 37 }
 38
 39 double solve(Point_t p) {
 40     int i, j, k;
 41     double ret = INF;
 42
 43     for (i=0; i<n; ++i) {
 44         ret = min(ret, Length(p, points[i]));
 45     }
 46
 47     return ret;
 48 }
 49
 50 int main() {
 51     int t;
 52     int i, j, k;
 53     Point_t p, pp;
 54     double step, angle;
 55     double ans, tmp;
 56
 57     #ifndef ONLINE_JUDGE
 58         freopen("data.in", "r", stdin);
 59     #endif
 60
 61     scanf("%d", &t);
 62     while (t--) {
 63         scanf("%lf %lf %d", &X, &Y, &n);
 64         for (i=0; i<n; ++i)
 65             scanf("%lf %lf", &points[i].x, &points[i].y);
 66         for (i=0; i<MAXM; ++i) {
 67             rpoints[i].x = (rand()%1000+1)/1000.0*X;
 68             rpoints[i].y = (rand()%1000+1)/1000.0*Y;
 69             rdis[i] = solve(rpoints[i]);
 70         }
 71         step = max(X, Y)/sqrt(1.0*n);
 72         while (step > eps) {
 73             for (i=0; i<MAXM; ++i) {
 74                 p = rpoints[i];
 75                 for (j=0; j<MAXM; ++j) {
 76                     angle = (rand()%1000+1)/1000.*10*PI;
 77                     pp.x = p.x + cos(angle)*step;
 78                     pp.y = p.y + sin(angle)*step;
 79                     if (check(pp))
 80                         continue;
 81                     tmp = solve(pp);
 82                     if (tmp > rdis[i]) {
 83                         rpoints[i] = pp;
 84                         rdis[i] = tmp;
 85                     }
 86                 }
 87             }
 88             step *= next;
 89         }
 90         double ans = -1.0;
 91         k = 0;
 92         for (i=0; i<MAXM; ++i) {
 93             if (rdis[i] > ans) {
 94                 ans = rdis[i];
 95                 k = i;
 96             }
 97         }
 98         printf("The safest point is (%.1lf, %.1lf).\n", rpoints[k].x, rpoints[k].y);
 99     }
100
101     return 0;
102 }