017.cpp

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#include <iostream>
using namespace std;

//x,one,two,three,four,five,six,seven,eight,nine
unsigned short unit_digits[] = { 0, 3, 3, 5, 4, 4, 3, 5, 5, 4 };

//x,ten,twenty,thirty,forty,fifty,sixty,seventy,eighty,ninety
unsigned short tenth_digits[] = { 0, 3, 6, 6, 5, 5, 5, 7, 6, 6 };

//ten,eleven,twelve,thirteen,fourteen,fifteen,sixteen,seventeen,eighteen,nineteen
unsigned short special[] = { 3, 6, 6, 8, 8, 7, 7, 9, 8, 8 };

unsigned
letters (unsigned k)
{
  unsigned sum = 0;
  if (k >= 100)
    {
      sum += unit_digits[k / 100] + 7;  //one hundred ...
      k %= 100;
      if (k > 0)
        sum += 3;               //...and...
    }
  if (k >= 20)
    {
      sum += tenth_digits[k / 10] + unit_digits[k % 10];        //...fourty one
      return sum;
    }
  else if (k >= 10)             //special case
    {
      sum += special[k % 10];   //...eleven
      return sum;
    }
  else
    {
      sum += unit_digits[k];    //...one
      return sum;
    }
}
int
main ()
{
  unsigned sum_of_letters = 0;
  for (unsigned k = 1; k <= 999; k++)
    sum_of_letters += letters (k);

  sum_of_letters += 3 + 8;      //one thousand
  cout << sum_of_letters << endl;
  return 0;
}