uVA 3n+1 problem

hotpo.cpp

/* Comment next line if your implementation doesn't support TR1
   It will then use STL's map instead of TR1's unordered_map,
   thus will be a little slow (map take worst case log(N) access time)
   If you don't care about memory, the solution can be sped up using arrays
   instead of std::map
*/
#define TR1
#include <iostream>
#ifdef TR1
#include <tr1/unordered_map>
std::tr1::unordered_map<unsigned int,unsigned int> hopto_lengths;
std::tr1::unordered_map<unsigned int, unsigned int>::iterator it;
#else
#include <map>
std::map<unsigned int,unsigned int> hopto_lengths;
std::map<unsigned int, unsigned int>::iterator it;
#endif

unsigned int hotpo_len(unsigned int n, unsigned int currlen = 1)
{ 
  if (n==1) return currlen;
  it = hopto_lengths.find(n);
  if (it != hopto_lengths.end())
    return it->second+currlen;
  else
    {
      //      std::cout<<"Calculating hotpo_len("<<n<<")\n";
      unsigned int result;
      if(!(n%2))
	result = hotpo_len(n/2,currlen+1);
      else
	result = hotpo_len(3*n+1,currlen+1);
      hopto_lengths[n] = result - currlen;
      return result;
    }
}
unsigned int max_hotpo(unsigned int i, unsigned int j)
{
  unsigned int max = hotpo_len(i);
  if (i >j)
    {
      return max_hotpo(j,i);
    }
  while ( ++i <= j )
    { 
      unsigned int curr = hotpo_len(i);
      // std::cout<<"i="<<i<<" hotpo(i)="<<curr<<std::endl;
      if(curr > max)
	max=curr;
    }
  return max;
}


int main()
{
  unsigned int i,j,r;
  while(std::cin>>i>>j)
    {
      std::cout<<i<<" "<<j<<" "<< max_hotpo(i,j)<<'\n';
    }

}