/*
 * list-02.cc    Standard Library, std::list, exercise 2.
 */
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <fstream>
#include <iterator>
#include <list>
using namespace std;

template<typename T>
struct greatest_common_divisor
{
   T operator()(const T& a, const T& b) const 
   { 
      return a == 0 ? b : (*this)(b % a, a);  // recursive call...
   }

   typedef T result_type;
   typedef T first_argument_type;
   typedef T second_argument_type;
};

template<typename InputIterator>
void output_three_columns(ostream& os, int width, 
			  InputIterator first1, InputIterator last1, 
			  InputIterator first2, 
			  InputIterator first3)
{
   while (first1 != last1)
   {
      os << setw(width) << *first1++ 
	 << setw(width) << *first2++ 
	 << setw(width) << *first3++ << '\n';
   }
}

int main(int argc, char* argv[])
{
   if (argc != 2) 
   {
      cout << "usage: argv[0] inputfile" << endl;
      return 1;
   }

   ifstream input(argv[1]);

   if (! input) 
   {
      cout << "can not open input file " << argv[1] << '\n';
      return 2;
   }

   list<int> list1, list2, gcd_list;
   int       x;

   while (input >> x) 
   {
      list1.push_back(x);
      input >> x;
      list2.push_back(x);
   }
   input.close();

   transform(begin(list1), end(list1), begin(list2), 
	     back_inserter(gcd_list), greatest_common_divisor<int>());

   cout << setw(8) << "First" << setw(8) << "Second" << setw(8) << "GCD\n\n";
   output_three_columns(cout, 8, begin(list1), end(list1), begin(list2), 
			begin(gcd_list));
   return 0;
}