Euler 017 c++ Solution

Problem

If the numbers 1 to 5 are written out in words: one, two, three, four, five, then there are \(3 + 3 + 5 + 4 + 4 = 19\) letters used in total.

If all the numbers from 1 to 1000 (one thousand) inclusive were written out in words, how many letters would be used?

NOTE: Do not count spaces or hyphens. For example, 342 (three hundred and forty-two) contains 23 letters and 115 (one hundred and fifteen) contains 20 letters. The use of “and” when writing out numbers is in compliance with British usage.

Answer: 21124

Solution

euler017.cpp

#include <iostream>

template <int n> int count_letter()
{
  int x = 0;
  if( n < 100 ){
    return count_letter<(n/10)*10>() + count_letter<n%10>();
  }

  x = (count_letter<n/100>()+7);//+count_letter<100>());
  if( 0 != (n%100)){
    x += 3 + count_letter<n-((n/100)*100)>();
  }
  return x;
}

template <> int count_letter<0>(){return 0;}
template <> int count_letter<1>(){return 3;}    // one
template <> int count_letter<2>(){return 3;}    // two
template <> int count_letter<3>(){return 5;}    // three
template <> int count_letter<4>(){return 4;}    // four
template <> int count_letter<5>(){return 4;}    // five
template <> int count_letter<6>(){return 3;}    // six
template <> int count_letter<7>(){return 5;}    // seven
template <> int count_letter<8>(){return 5;}    // eight
template <> int count_letter<9>(){return 4;}    // nine
template <> int count_letter<10>(){return 3;}   // ten
template <> int count_letter<11>(){return 6;}   // eleven
template <> int count_letter<12>(){return 6;}   // twelve
template <> int count_letter<13>(){return 8;}   // thirteen
template <> int count_letter<14>(){return 8;}   // fourteen
template <> int count_letter<15>(){return 7;}   // fifteen
template <> int count_letter<16>(){return 7;}   // sixteen
template <> int count_letter<17>(){return 9;}   // seventeen
template <> int count_letter<18>(){return 8;}   // eighteen
template <> int count_letter<19>(){return 8;}   // nineteen
template <> int count_letter<20>(){return 6;}   // twenty
template <> int count_letter<30>(){return 6;}   // thirty
template <> int count_letter<40>(){return 5;}   // forty
template <> int count_letter<50>(){return 5;}   // fifty
template <> int count_letter<60>(){return 5;}   // sixty
template <> int count_letter<70>(){return 7;}   // seventy
template <> int count_letter<80>(){return 6;}   // eighty
template <> int count_letter<90>(){return 6;}   // ninety
template <> int count_letter<100>(){return 10;}  // onehundred
template <> int count_letter<1000>(){return 11;} // onethousand

static int g_letter_count = 0;

template<int from,int to> struct mp_for
{
  void operator()()
  {
    g_letter_count += count_letter<from>();
    mp_for<from+1,to>()();
  }
};

// Recursive template stop
template<int from> struct mp_for<from,from>
{
  void operator()(){};
};

#if ! defined UNITTEST_MODE
int main(int argc, char const *argv[]) {
  mp_for<1,1001>()(); // Template recursion stops at <1001,1001>
  std::cout << "Answer: " << g_letter_count << std::endl;
  return 0;
}
#endif // #if ! defined UNITTEST_MODE

Euler 017 c++ Solution

Problem

Solution

See Also