Yan Cui
I help clients go faster for less using serverless technologies.
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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
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