Euler Project #17

euler_project_17.py

'''
See http://projecteuler.net/index.php?section=problems&id=17
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.
'''
def num_letters(number):
    digit_len = {1:3, 2:3, 3:5, 4:4, 5:4, 6:3, 7:5, 8:5, 9:4}
    first_two_len = {10:3, 11:6, 12:6, 13:8, 14:8, 15:7, 16:7, 17:9, 18:8, 19:8, 20:6, 30:6, 40:5, 50:5, 60:5, 70:7, 80:6, 90:6, 00:0}
    letter_count = 0
    if(number < 10):
        return digit_len[number]
        
    first_two = int("".join(list(str(number))[-2:]))
    if(first_two not in first_two_len):
        letter_count += digit_len[int(list(str(number))[-1])]
        letter_count += first_two_len[int(list(str(number))[-2]+'0')]
    else:
        letter_count += first_two_len[first_two]

    hundreds = int(str(number).rjust(3,'0')[-3])
    if(hundreds > 0):
        if(first_two > 0):
            #add the and in 'hundred and'
            letter_count += 3
        letter_count += digit_len[hundreds] + 7

    first_three = first_two = int("".join(list(str(number).rjust(3,'0'))[-3:]))
    thousands = int(str(number).rjust(4,'0')[-4])
    if(thousands > 0):
        if(first_three > 0):
            #add the and in 'thousand and'
            letter_count += 3
        letter_count += digit_len[thousands] + 8
    
    return letter_count

print(reduce(lambda x,y:x+y, (num_letters(x) for x in range(1,1001))))