目录

• 题目链接
• 题解
• 代码

题目链接

loj#2076. 「JSOI2016」炸弹攻击

题解

模拟退火
退火时，由于答案比较小，但是温度比较高
所以在算exp时最好把相差的点数乘以一个常数让选取更差的的概率降低

代码

#include<ctime>
#include<cmath>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define gc getchar()
#define pc putchar
inline int read() {
     int x = 0,f = 1;
     char c = gc;
     while(c < '0' || c > '9') c  =gc;
     while(c <= '9' && c >= '0') x = x * 10 + c - '0',c = gc;
     return x * f;
}
void print(int x) {
    if(x < 0) {
        pc('-');
        x = -x;
    }
    if(x >= 10) print(x / 10);
    pc(x % 10 + '0');
}
const int maxn = 100007;
int n,m; double R;
double X[maxn],Y[maxn],r[maxn],p[maxn],q[maxn];
double rd() {
    return (double) rand() / RAND_MAX;
}
void randpos(double &x,double & y){
    x = 2 * R * rd() - R;
    y = 2 * R * rd() - R;
}
#define dt 0.998
#define eps 1e-2
double dis(double x,double y,double x1,double y1) {
    return std::sqrt((x - x1) * (x - x1) + (y - y1) * (y - y1));
}
int calc(double x,double y) {
    int ret = 0;
    double tr = R;
    for(int i = 1;i <= n;++ i) {
        tr = std::min(tr,dis(X[i],Y[i],x,y) - r[i]);
    }
    if(r < 0) return 0;
    for(int i = 1;i <= m;++ i)
        if(dis(x,y,p[i],q[i]) <= tr) ret ++;
    return ret;
}
int solve(double x,double y) {
    int mx = calc(x,y);
    int now = mx;
    double T = R;
    for(;T > eps;T *= dt) {
        double nt = T + 0.1;
        double nx = x + (2.0 * nt) * rd() - nt,ny = y + (2 * nt) * rd() - nt;
        int nans = calc(nx,ny);
        if(nans > mx || exp(1e4 * (nans - now) / T) > rd()) x = nx,y = ny,now = nans;
        mx = std::max(mx,now);
    }
    return mx;
}
int main() {
    srand(19991206);
    scanf("%d%d%lf",&n,&m,&R);
    for(int i = 1;i <= n;++ i)
        scanf("%lf%lf%lf",&X[i],&Y[i],&r[i]);
    for(int i = 1;i <= m;++ i)
        scanf("%lf%lf",p + i,q + i);
    int ans = 0 ;
    double px,py;
    for(int i = 1;i <= 20;++ i) {
        randpos(px,py);
        ans = std::max(ans,solve(px,py));
    }
    print(ans);
    pc('\n');
} 

原文地址：https://www.cnblogs.com/sssy/p/9726267.html