#lang racket

(require advent-of-code
         (only-in algorithms sliding))

(define buffer (fetch-aoc-input (find-session) 2022 6))

(define (find-marker data type)
  (define n
    (case type
      [(start-of-packet) 4]
      [(start-of-message) 14]))
  (for/first ([chunk (in-list (sliding (string->list data) n))]
              [i (in-naturals n)]
              #:unless (check-duplicates chunk))
    i))

;; part 1
(find-marker buffer 'start-of-packet)

;; part 2
(find-marker buffer 'start-of-message)