poj 2420 A Star not a Tree? —— 模拟退火
题目:http://poj.org/problem?id=2420
给出 n 个点的坐标,求费马点;
上模拟退火。
代码如下:
#include<iostream> #include<cstdio> #include<cstring> #include<algorithm> #include<cstdlib> #include<ctime> #include<cmath> #define eps 1e-17 #define dt 0.99 using namespace std; typedef double db; int const xn=105; int n,xx[xn],yy[xn]; db ansx,ansy,ans; int rd() { int ret=0,f=1; char ch=getchar(); while(ch<'0'||ch>'9'){if(ch=='0')f=0; ch=getchar();} while(ch>='0'&&ch<='9')ret=(ret<<3)+(ret<<1)+ch-'0',ch=getchar(); return f?ret:-ret; } db dist(db x,db y,db a,db b){return sqrt((x-a)*(x-a)+(y-b)*(y-b));} db cal(db x,db y) { db ret=0; for(int i=1;i<=n;i++)ret+=dist(x,y,xx[i],yy[i]); return ret; } void SA() { db T=10000,x=ansx,y=ansy,lst=ans,tx,ty,tmp; while(T>eps) { tx=x+(rand()*2-RAND_MAX)*T; ty=y+(rand()*2-RAND_MAX)*T; tmp=cal(tx,ty); db delt=tmp-lst; if(delt<0||exp(delt/T)*RAND_MAX<rand())x=tx,y=ty,lst=tmp; if(tmp<ans)ansx=tx,ansy=ty,ans=tmp; T*=dt; } } int main() { n=rd(); int sx=0,sy=0; for(int i=1;i<=n;i++)xx[i]=rd(),yy[i]=rd(),sx+=xx[i],sy+=yy[i]; ansx=1.0*sx/n; ansy=1.0*sy/n; ans=cal(ansx,ansy); SA(); SA(); SA(); printf("%.0lf\n",ans); return 0; }