【POJ】2420 A Star not a Tree?

#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <algorithm>
using namespace std;
const int N=105;
struct P { int x, y; }a[N];
int n;
inline int rand(int x, int y) { return x+(rand()%(y-x+1)); }
inline double sqr(double x) { return x*x; }
inline double dis(double x1, double y1, double x2, double y2) { return sqrt(sqr(x1-x2)+sqr(y1-y2)); }
inline double getdis(double x, double y) {
	double ret=0;
	for(int i=0; i<n; ++i) ret+=dis(x, y, a[i].x, a[i].y);
	return ret;
}
double getnode(double x, double y, double T, double &xx, double &yy) {
	double tx, ty, dis, ret=1e300;
	for(int i=0; i<50; ++i) {
		tx=x+(rand(-100, 100)/100)*T;
		ty=y+(rand(-100, 100)/100)*T;
		dis=getdis(tx, ty);
		if(dis<ret) {
			ret=dis;
			xx=tx;
			yy=ty;
		}
	}
	return ret;
}
int main() {
	srand(1998);
	while(~scanf("%d", &n)) {
		double x=0, y=0, T=1e20, dE, tans, ans, nans, xx, yy;
		for(int i=0; i<n; ++i) scanf("%d%d", &a[i].x, &a[i].y), x+=a[i].x, y+=a[i].y;
		x/=n; y/=n;
		nans=ans=getdis(x, y);
		while(T>0.01) {
			tans=getnode(x, y, T, xx, yy);
			dE=nans-tans;
			if(dE>=0 || log(dE/T)>(rand(1, 99999)/100000)) {
				nans=tans; x=xx; y=yy; ans=min(ans, nans);
			}
			T*=0.9;
		}
		printf("%.0f\n", ans);
	}
	return 0;
}