【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-3;
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<0 || p.x>=X || p.y<0 || 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=0; 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=0; i<n; ++i)
            scanf("%lf %lf", &points[i].x, &points[i].y);
        for (i=0; i<MAXM; ++i) {
            rpoints[i].x = (rand()%1000+1)/1000.0*X;
            rpoints[i].y = (rand()%1000+1)/1000.0*Y;
            rdis[i] = solve(rpoints[i]);
        }
        step = max(X, Y)/sqrt(1.0*n);
        while (step > eps) {
            for (i=0; i<MAXM; ++i) {
                p = rpoints[i];
                for (j=0; j<MAXM; ++j) {
                    angle = (rand()%1000+1)/1000.*10*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 = 0;
        for (i=0; i<MAXM; ++i) {
            if (rdis[i] > ans) {
                ans = rdis[i];
                k = i;
            }
        }
        printf("The safest point is (%.1lf, %.1lf).
", rpoints[k].x, rpoints[k].y);
    }
    
    return 0;
}