#= Created on 24 Jul 2021 @author: David Doblas Jiménez @email: daviddoji@pm.me Solution for Problem 14 of Project Euler https://projecteuler.net/problem=14 =# function chain_length(n)#, terms) length = 0 while n > 1 n = iseven(n) ? n >> 1 : 3n + 1 length += 1 end return length end function Problem14() #= The following iterative sequence is defined for the set of positive integers: n → n/2 (n is even) n → 3n + 1 (n is odd) Using the rule above and starting with 13, we generate the following sequence: 13 → 40 → 20 → 10 → 5 → 16 → 8 → 4 → 2 → 1 It can be seen that this sequence (starting at 13 and finishing at 1) contains 10 terms. Although it has not been proved yet (Collatz Problem), it is thought that all starting numbers finish at 1. Which starting number, under one million, produces the longest chain? NOTE: Once the chain starts the terms are allowed to go above one million. =# ans = 0 limit = 1_000_000 score = 0 for i in 1:2:limit # no need to check even numbers longest = chain_length(i) if longest > score score = longest ans = i end end return ans end println("Time to evaluate Problem 14:") @time Problem14() println("") println("Result for Problem 14: ", Problem14())