hdu 5017 模拟退火求最值

题意：

给一个椭圆：

然后求原点到这个椭圆距离最小的点的距离是多少。

解析：

依旧用模拟退火。

修改了一个地方，初始温度从100改到了1，就行了。

之前的也修改了。

选z的时候，选离远点近的那个点就行了。

代码：

#pragma comment(linker, "/STACK:1677721600")
#include <map>
#include <set>
#include <cmath>
#include <queue>
#include <stack>
#include <vector>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <climits>
#include <cassert>
#include <iostream>
#include <algorithm>
#define pb push_back
#define mp make_pair
#define LL long long
#define lson lo,mi,rt<<1
#define rson mi+1,hi,rt<<1|1
#define Min(a,b) ((a)<(b)?(a):(b))
#define Max(a,b) ((a)>(b)?(a):(b))
#define mem(a,b) memset(a,b,sizeof(a))
#define FIN freopen("in.txt", "r", stdin)
#define FOUT freopen("out.txt", "w", stdout)
#define rep(i,a,b) for(int i=(a); i<=(b); i++)
#define dec(i,a,b) for(int i=(a); i>=(b); i--)

using namespace std;
const int mod = 1e9 + 7;
const double ee = exp(1.0);
const int inf = 0x3f3f3f3f;
const int maxn = 1e6 + 10;
const double pi = acos(-1.0);
const LL iinf = 0x3f3f3f3f3f3f3f3f;

int readT()
{
    char c;
    int ret = 0,flg = 0;
    while(c = getchar(), (c < '0' || c > '9') && c != '-');
    if(c == '-') flg = 1; else ret = c ^ 48;
    while( c = getchar(), c >= '0' && c <= '9') ret = ret * 10 + (c ^ 48);
    return flg ? - ret : ret;
}

const double eps = 1e-8;    //搜索停止条件
const double delta = 0.98;  //温度下降速度
const int initT = 1;      //初始温度

int dir[][2] = {{1, 0}, {0, 1}, {-1, 0}, {0, -1}};
// {1, 1}, {1, -1}, {-1, 1}, {-1, -1}

double a, b, c, d, e, f;

struct Point
{
    double x, y, z;
    Point(){}
    Point(double _x, double _y, double _z)
    {
        x = _x;
        y = _y;
        z = _z;
    }
};

double dist(Point a)
{
    return sqrt(a.x * a.x + a.y * a.y + a.z * a.z);
}

double getZ(double x, double y)
{
    double A = c;
    double B = e * x + d * y;
    double C = a * x * x + b * y * y + f * x * y - 1;

    double delta = B * B - 4 * A * C;

    if (delta < 0)
    {
        return inf;
    }

    double z1 = (-B + sqrt(delta)) / 2 / A;
    double z2 = (-B - sqrt(delta)) / 2 / A;

    double res = (fabs(z1) < fabs(z2)) ? z1 : z2;
    return res;
}

double solve()
{
    double t = initT;
    double ans = inf;
    Point star(0, 0, 0);
    star.z = getZ(star.x, star.y);

    while (eps < t)
    {
        bool flag = true;
        while (flag)
        {
            flag = false;
            rep(i, 0, 7)
            {
                Point now;
                now.x = star.x + dir[i][0] * t;
                now.y = star.y + dir[i][1] * t;
                now.z = getZ(now.x, now.y);
                if (now.z == inf)
                    continue;
                double t = dist(now);
                if (t < ans)
                {
                    ans = t;
                    star = now;
                    flag = true;
                }
            }
        }
        t *= delta;
    }
    return ans;
}

int main()
{
    #ifdef LOCAL
    FIN;
    #endif // LOCAL
    while (~scanf("%lf%lf%lf%lf%lf%lf", &a, &b, &c, &d, &e, &f))
    {
        printf("%.8lf\n", solve());
    }
    return 0;
}