#=
Created on 21 Jul 2021

@author: David Doblas Jiménez
@email: daviddoji@pm.me

Solution for Problem 012 of Project Euler
https://projecteuler.net/problem=12
=#

using BenchmarkTools


function num_divisors(number::Int64)
    res = isqrt(number)
    return 2 * count(number % i == 0 for i = 1:res) - (res^2 == number)
end


function Problem012()
    #=
     The sequence of triangle numbers is generated by adding the natural
    numbers. So the 7th triangle number would be:
    1 + 2 + 3 + 4 + 5 + 6 + 7 = 28.

    The first ten terms would be:
    1, 3, 6, 10, 15, 21, 28, 36, 45, 55, ...

    Let us list the factors of the first seven triangle numbers:

     1: 1
     3: 1,3
     6: 1,2,3,6
    10: 1,2,5,10
    15: 1,3,5,15
    21: 1,3,7,21
    28: 1,2,4,7,14,28

    We can see that 28 is the first triangle number to have over five divisors.

    What is the value of the first triangle number to have over five hundred
    divisors?
    =#

    ans = 0
    for number in Iterators.countfrom(1)
        ans += number
        if num_divisors(ans) > 500
            return ans
        end
    end
end


println("Took:")
@btime Problem012()
println("")
println("Result for Problem $(lpad(12, 3, "0")): ", Problem012())