#!/usr/bin/env python3

# The nth term of the sequence of triangle numbers is given by, tn = ½n(n+1); so the first ten triangle numbers are:
#
# 1, 3, 6, 10, 15, 21, 28, 36, 45, 55, ...
#
# By converting each letter in a word to a number corresponding to its alphabetical position and adding these values we form a word value.
# For example, the word value for SKY is 19 + 11 + 25 = 55 = t10. If the word value is a triangle number then we shall call the word a triangle word.
#
# Using p042_words.txt (right click and 'Save Link/Target As...'), a 16K text file containing nearly two-thousand common English words,
# how many are triangle words?

import sys
from timeit import default_timer


def is_triang(n):
    i = 1
    j = 1

    while j <= n:
        if n == j:
            return True
        i = i + 1
        j = j + i

    return False


def main():
    start = default_timer()

    try:
        with open('p042_words.txt', 'r', encoding='utf-8') as fp:
            words = list(fp.readline().replace('"', '').split(','))
    except FileNotFoundError:
        print('Error while opening file p042_words.txt')
        sys.exit(1)

    count = 0

#   For each word, calculate its value and check if it's a triangle number.
    for word in words:
        value = 0
        l = len(word)

        for j in range(l):
            value = value + ord(word[j]) - ord('A') + 1

        if is_triang(value):
            count = count + 1

    end = default_timer()

    print('Project Euler, Problem 42')
    print(f'Answer: {count}')

    print(f'Elapsed time: {end - start:.9f} seconds')


if __name__ == '__main__':
    main()