bzoj3680 吊打XXX

Posted 2020-09-20 逢山开路 遇水架桥

传送门：http://www.lydsy.com/JudgeOnline/problem.php?id=3680

【题解】

模拟退火

getdis瞎推推，猜猜就猜出来了吧。。

前面没看n的范围设N=20, T=20作死

改成T=5,N=8就10s刚好过了

# 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 = 5e4 + 10;
const int mod = 1e9+7;

# define RG register
# define ST static

int n, w[M];
double minx, miny, maxx, maxy;
struct P {
    double x, y;
    double dis;
    P() {}
    P(double x, double y, double dis) : x(x), y(y), dis(dis) {}
}p[M];

namespace SA { 
    const int RAD = 1000;
    const int T = 5, N = 8;
    const double eps = 1e-3, DEC = 0.9, ACCEPT_DEC = 0.5;
     
    inline double rand01() {
        return rand() % (RAD + 1) / (1.0 * RAD);
    }
    
    inline double getdis(double x, double y) {
        double ret = 0;
        for (int i=1; i<=n; ++i) {
            ret += sqrt((p[i].x-x)*(p[i].x-x)+(p[i].y-y)*(p[i].y-y)) * w[i]; 
        }
        return ret;
    }
    
    inline P randpoint(double xl, double yl, double xr, double yr) {
        double x = (xr-xl) * rand01() + xl, y = (yr-yl) * rand01() + yl; 
        return P(x, y, getdis(x, y));    
    }
    
    P res[N + 5]; 
    
    inline P main() {
        double temper = sqrt(1.0 * (maxx-minx)*(maxx-minx) + 1.0 * (maxy-miny)*(maxy-miny)), accept = 0.6;
        for (int i=1; i<=N; ++i) res[i] = randpoint(minx, miny, maxx, maxy);
        while(temper > eps) {
            for (int i=1; i<=N; ++i)
                for (int j=1; j<=T; ++j) {
                    P t = randpoint(max(minx, res[i].x-temper), max(miny, res[i].y-temper), min(maxx, res[i].x+temper), min(maxy, res[i].y+temper));
                    if(t.dis < res[i].dis) res[i] = t;
                    else if(rand01() <= accept) res[i] = t;
                }
            temper *= DEC;
            accept *= ACCEPT_DEC;    
        }
        P ans = res[1]; 
        for (int i=2; i<=N; ++i)
            if(ans.dis > res[i].dis) ans = res[i];
        return ans;
    }
}


int main() {
    minx = miny = 1e9, maxx = maxy = -1e9;
    cin >> n;
    for (int i=1, x, y; i<=n; ++i) {
        scanf("%d%d%d", &x, &y, w+i);
        minx = min(minx, (double)x); maxx = max(maxx, (double)x);
        miny = min(miny, (double)y); maxy = max(maxy, (double)y); 
        p[i] = P((double)x, (double)y, 0);
    }
    P ans = SA::main(); 
    printf("%.3lf %.3lf\n", ans.x, ans.y); 
    return 0;
}

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