in my attempt to teach myself Julia, I’m solving Project Euler problems. The following code works and give the correct answer, although I was expecting better performance, as the time is similar to what I got using Python. Here it is the code:
function chain_length(n, terms) length = 0 while n != 1 if haskey(terms, n) length += terms[n] break end if n % 2 == 0 n = n / 2 else n = 3n + 1 end 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 terms = Dict() for i in 1:limit terms[i] = chain_length(i, terms) if terms[i] > score score = terms[i] ans = i end end return ans end
thanks in advance.