Check out my new course Learn you some Lambda best practice for great good! and learn the best practices for performance, cost, security, resilience, observability and scalability.
It is possible to write ten as the sum of primes in exactly five different ways:
7 + 3
5 + 5
5 + 3 + 2
3 + 3 + 2 + 2
2 + 2 + 2 + 2 + 2
What is the first value which can be written as the sum of primes in over five thousand different ways?
// generate all prime numbers under <= this max let max = 1000 let mutable primeNumbers =  // only check the prime numbers which are <= the square root of the number n let hasDivisor n = primeNumbers |> Seq.takeWhile (fun n' -> n' <= int(sqrt(double(n)))) |> Seq.exists (fun n' -> n % n' = 0) // only check odd numbers <= max let potentialPrimes = Seq.unfold (fun n -> if n > max then None else Some(n, n+2)) 3 // populate the prime numbers list for n in potentialPrimes do if not(hasDivisor n) then primeNumbers <- primeNumbers @ [n] let isPrime n = if n = 1 then false else not(hasDivisor(n)) // implement the coin change algorithm let rec count n m (coins:int list) = if n = 0 then 1 else if n < 0 then 0 else if (m <= 0 && n >= 1) then 0 else (count n (m-1) coins) + (count (n-coins.[m-1]) m coins) let answer = let tuple = Seq.unfold (fun state -> Some(state, state+1)) 10 |> Seq.map (fun n -> (n, primeNumbers |> Seq.filter (fun n' -> n' < n) |> Seq.cache)) |> Seq.filter (fun (n, l) -> count n (Seq.length l) (Seq.toList l) > 5000) |> Seq.head fst tuple
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Here is a complete list of all my posts on serverless and AWS Lambda. In the meantime, here are a few of my most popular blog posts.
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