poj1379 Run Away

传送门：http://poj.org/problem?id=1379

【题解】

题目大意：求(0,0)->(X,Y)内的一个点，使得这个点到给定的n个点的最小距离最大。

模拟退火

一开始可以先把4个顶点加入。

调调参就过样例了。

然后就过了

# include <math.h>
# include <stdio.h>
# include <stdlib.h>
# include <string.h>
# include <iostream>
# include <algorithm>
// # include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
const int M = 5e5 + ;
const int mod = 1e9+;
const double pi = acos(-1.0);

# define RG register
# define ST static

double X, Y;
int n;
struct pa {
    double x, y;
    double dis;
    pa() {}
    pa(double x, double y, double dis) : x(x), y(y), dis(dis) {}
}a[M];

namespace SA {
    const double eps = 1e-, DEC = 0.9, ACCEPT_DEC = 0.5;
    const int N = , T = , RAD = ;
    inline double rand01() {
        return rand() % (RAD + ) / (1.0 * RAD);
    }
    inline double getdist(double x, double y) {
        double ret = 1e18;
        for (int i=; i<=n; ++i)
            ret = min(ret, (x-a[i].x)*(x-a[i].x)+(y-a[i].y)*(y-a[i].y));
        return ret;
    }
    inline pa randpoint(double px, double py, double qx, double qy) {
        double x = (qx - px) * rand01() + px, y = (qy - py) * rand01() + py;
        return pa(x, y, getdist(x, y));
    }
    pa res[N + ];
    inline pa main() {
        res[] = pa(, , getdist(, ));
        res[] = pa(X, , getdist(X, ));
        res[] = pa(, Y, getdist(, Y));
        res[] = pa(X, Y, getdist(X, Y));
        for (int i=; i<=N; ++i) {
            double x = rand01() * X;
            double y = rand01() * Y;
            res[i] = pa(x, y, getdist(x, y));
        }
        double temper = max(X, Y), accept = 0.6;
        while(temper > eps) {
            for (int i=; i<=N; ++i) {
                for (int j=; j<=T; ++j) {
                    pa t = randpoint(max(res[i].x - temper, 0.0), max(res[i].y - temper, 0.0), min(res[i].x + temper, X), min(res[i].y + temper, Y));
                    if( <= t.x && t.x <= X &&  <= t.y && t.y <= Y) {
                        if(t.dis > res[i].dis) res[i] = t;
                        else if(rand01() <= accept) res[i] = t;
                    }
                }
            }
            temper *= DEC;
            accept *= ACCEPT_DEC;
        }
        pa ans;
        ans.dis = ;
        for (int i=; i<=N; ++i)
            if(res[i].dis > ans.dis) ans = res[i];
        return ans;
    }
}

int main() {
    srand();
    int T; cin >> T;
    while(T--) {
        cin >> X >> Y >> n;
        for (int i=; i<=n; ++i) scanf("%lf%lf", &a[i].x, &a[i].y);
        pa ans = SA::main();
        printf("The safest point is (%.1f, %.1f).\n", ans.x, ans.y);
    }

    return ;
}