Project Euler – Problem 52 Solution

Problem

It can be seen that the number, 125874, and its double, 251748, contain exactly the same digits, but in a different order.

Find the smallest positive integer, x, such that 2x, 3x, 4x, 5x, and 6x, contain the same digits.

Solution

// check if two numbers are permutations of the same set of digits
let isPermutation number1 number2 =
    let str1 = number1.ToString().ToCharArray() |> Array.sort
    let str2 = number2.ToString().ToCharArray() |> Array.sort

    if str1.Length <> str2.Length then false
    else Array.forall2 (fun x y -> x = y) str1 str2

let answer =
    Seq.unfold (fun state -> Some(state, state + 1)) 1
    |> Seq.filter (fun n -> 
        [2..6] |> List.map (fun x -> x * n) |> List.forall (fun xn -> isPermutation xn n))
    |> Seq.head

Enjoy what you’re reading? Subscribe to my newsletter and get more content on AWS and serverless technologies delivered straight to your inbox.


Yan Cui

I’m an AWS Serverless Hero and the author of Production-Ready Serverless. I have run production workload at scale in AWS for nearly 10 years and I have been an architect or principal engineer with a variety of industries ranging from banking, e-commerce, sports streaming to mobile gaming. I currently work as an independent consultant focused on AWS and serverless.

You can contact me via Email, Twitter and LinkedIn.

Hire me.


Check out my new course, Complete Guide to AWS Step Functions.

In this course, we’ll cover everything you need to know to use AWS Step Functions service effectively. Including basic concepts, HTTP and event triggers, activities, design patterns and best practices.

Get Your Copy