AdventOfCode2025.Day02.fsx

AdventOfCode2025.Day02.fsx

#time "on"

open System
open System.IO

let input =
    File.ReadAllText(__SOURCE_DIRECTORY__ + "/../data/input02.txt")

let ranges = 
    input.Split(',') 
    |> Seq.map(fun x -> x.Split('-') |> Seq.map int64 |>  Seq.toList |> fun x -> x[0], x[1]) 
    |> Seq.toList

// Part One (28844599675)
let rec findDuplicates1 (start: int64) (stop: int64) result = 
    if start > stop then
        result
    else
        let s = start.ToString()
        let result = 
            if s.Length % 2 = 0 && s.Substring(0, s.Length/2) = s.Substring(s.Length/2) then
                s :: result
            else
                result
        findDuplicates1 (start+1L) stop result

ranges
|> List.fold (fun result range ->
    let start, stop = range
    findDuplicates1 start stop result) []
|> List.map int64
|> List.sum

// Part Two (4174379265)
let hasN (s: string) n =
    let rec areDuplicates ndx result =
        if (ndx+1) * n = s.Length then
            true
        else
            if s.Substring(0, n) = s.Substring((ndx+1) * n, n) then
                areDuplicates (ndx+1) result
            else
                false
    s.Length % n = 0 && s.Length > n && areDuplicates 0 true

let rec findDuplicates2 (start: int64) (stop: int64) result = 
    if start > stop then
        result
    else
        let s = start.ToString()
        let result = 
            if [1..10] |> List.fold (fun result n -> result || hasN s n) false then
                s :: result
            else
                result
        findDuplicates2 (start+1L) stop result

ranges
|> List.fold (fun result (start, stop) ->
    findDuplicates2 start stop result) []
|> List.map int64
|> List.sum