#include <iostream>
#include <map>
#include <algorithm>
#include <memory>
//---------------------------------------------------------------------------
struct FunctionBase
{
  virtual const double GetY(const double x) const = 0;
  virtual ~FunctionBase() {} //Base class must have virtual destructor
};
//---------------------------------------------------------------------------
struct FunctionLogisticGrowth : public FunctionBase
{
  FunctionLogisticGrowth(const double r) : mR(r) {}

  const double GetY(const double x) const
  {
    //The discrete time version of the logistic growth equation
    //Assumes a K of 1.0
    return (mR * x * (1.0 - x));
  }
  const double mR;
};
//---------------------------------------------------------------------------
//From http://www.richelbilderbeek.nl/CppFindEquilibrium.htm
const int GetPeriod(
  const std::auto_ptr<const FunctionBase>& anyFunction,
  const double xZero,
  const int maxT)
{
  std::map<double,int> values; //value, time
  double x = xZero;
  for(int t=0; t!=maxT; ++t)
  {
    if (values.find(x)!=values.end())
    {
      //The previous time this value was found
      const int tPrev = values[x];
      //The distance between now and the previous time
      const int period = t-tPrev;
      return period;
    }
    //Map this population size to the time now
    values[x] = t;
    //Set the value to the next value
    x = anyFunction->GetY(x);
  }
  //Time too long
  return maxT;
}
//---------------------------------------------------------------------------
//From http://www.richelbilderbeek.nl/CppFindEquilibrium.htm
int main()
{
  //Of the logistic growth equation, determine the period length for
  //different values of intrinsic growth rate ('r')
  const int maxT = 100000;
  const double xZero = 0.1;
  for (double r = 0.1; r < 4.0; r+=0.001)
  {
    const std::auto_ptr<const FunctionBase> myFunction(new FunctionLogisticGrowth(r));
    std::cout << r << " : "
      << GetPeriod(myFunction,xZero,maxT) << std::endl;
  }
}