【计算几何】 HDOJ 5017 Ellipsoid

网上百度的题解。。。http://blog.csdn.net/accelerator_/article/details/39294451。。。模拟退火大发好。。。。

#include <iostream>  
#include <queue>  
#include <stack>  
#include <map>  
#include <set>  
#include <bitset>  
#include <cstdio>  
#include <algorithm>  
#include <cstring>  
#include <climits>
#include <cstdlib>
#include <cmath>
#include <time.h>
#define maxn 100005
#define maxm 40005
#define eps 1e-10
#define mod 1000000007
#define INF 1e9
#define lowbit(x) (x&(-x))
#define mp mark_pair
#define ls o<<1
#define rs o<<1 | 1
#define lson o<<1, L, mid  
#define rson o<<1 | 1, mid+1, R  
typedef long long LL;
//typedef int LL;
using namespace std;
LL qpow(LL a, LL b){LL res=1,base=a;while(b){if(b%2)res=res*base;base=base*base;b/=2;}return res;}
LL powmod(LL a, LL b){LL res=1,base=a;while(b){if(b%2)res=res*base%mod;base=base*base%mod;b/=2;}return res;}
void scanf(int &__x){__x=0;char __ch=getchar();while(__ch==' '||__ch=='\n')__ch=getchar();while(__ch>='0'&&__ch<='9')__x=__x*10+__ch-'0',__ch = getchar();}
LL gcd(LL _a, LL _b){if(!_b) return _a;else return gcd(_b, _a%_b);}
// head

int dir[8][2] = {{1, 0}, {-1, 0}, {0, 1}, {0, -1}, {1, 1}, {1, -1}, {-1, 1}, {-1, -1}};
double a, b, c, d, e, f;
double dist(double x, double y, double z)
{
	return sqrt(x * x + y * y + z * z);
}
double solve(double x, double y)
{
	double A = c;
	double B = d * y + e * x;
	double C = a * x * x + b * y * y + f * x * y - 1;
	double t = B * B - 4.0 * A * C;
	if(t < 0) return 1e10;
	double tt = sqrt(t);
	double z1 = (-B + tt) / A / 2;
	double z2 = (-B - tt) / A / 2;
	if(dist(x, y, z1) < dist(x, y, z2)) return z1;
	else return z2;
}
void work(void)
{
	double step = 1.0, next = 0.99;
	double x, y, z, xx, yy, zz;
	x = y = 0, z = sqrt(1.0 / c);
	while(step > eps) {
		for(int i = 0; i < 8; i++) {
			xx = x + step * dir[i][0];
			yy = y + step * dir[i][1];
			zz = solve(xx, yy);
			if(zz > INF) continue;
			if(dist(xx, yy, zz) < dist(x, y, z))
				x = xx, y = yy, z = zz;
		}
		step *= next;
	}
	printf("%.7f\n", dist(x, y, z));
}
int main(void)
{
	while(scanf("%lf%lf%lf%lf%lf%lf", &a, &b, &c, &d, &e, &f)!=EOF) work();
	return 0;
}