hdu 2899 Strange fuction——模拟退火

Posted 2021-01-16 narh

题目：http://acm.hdu.edu.cn/showproblem.php?pid=2899

还可三分。不过只写了模拟退火。

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<ctime>
#include<cmath>
#include<cstdlib>
#define db double
using namespace std;
const int nx[6]={0,7,6,3,2,1},c[6]={0,6,8,7,5,1};
const db dc=0.997,eps=1e-17;
int T;
db y,ans,px;
db pw(db x,int k){db ret=1;while(k){if(k&1)ret*=x;x*=x;k>>=1;}return ret;}
db calc(db x)
{
  db ret=0;
  for(int i=1;i<=4;i++)ret+=c[i]*pw(x,nx[i]);
  ret-=y*x; return ret;
}
db gtrd(db T){return (rand()*2-RAND_MAX)*T;}
void SA(db T)
{
  db x0=px,pr=ans,x,cr;
  while(T>eps)
    {
      x=x0+gtrd(T); if(x>100)x=100; if(x<0)x=0; cr=calc(x);
      if(cr<pr||exp((cr-pr)/T)*RAND_MAX<rand())
    {
      if(cr<ans)ans=cr,px=x;
      x0=x;pr=cr;
    }
      T*=dc;
    }
}
int main()
{
  srand(time(0));
  scanf("%d",&T);
  while(T--)
    {
      scanf("%lf",&y);
      px=50;ans=calc(px);
      for(int i=1;i<=2;i++)SA(10000);
      printf("%.4lf
",ans);
    }
  return 0;
}