#lang racket
(require rackunit)
(define input (file->lines "day01-input.txt"))
(define start-frequency 0)
(define (day01-part1)
(apply + start-frequency (map string->number input)))
(module+ test
(check-equal? (day01-part1) 486)) ; Correct answer for part1
(define (day01-part2 [freq-changes (map string->number input)]
[start-from start-frequency]
[seen-frequencies (list start-frequency)])
(define run-through
(for/fold ([seen seen-frequencies]
[current-freq start-from]
#:result seen)
([freq-change (in-list freq-changes)])
#:final (member (+ current-freq freq-change) seen)
(values (append seen (list (+ current-freq freq-change))) (+ current-freq freq-change))))
(cond
[(check-duplicates run-through)
(last run-through)]
[else
(day01-part2 freq-changes (last run-through) run-through)]))
(module+ test
(check-equal? (day01-part2 '(3 3 4 -2 -4)) 10)
(check-equal? (day01-part2 '(-6 3 8 5 -6)) 5)
(check-equal? (day01-part2 '(7 7 -2 -7 -4)) 14)
; Actually getting the correct answer for my input takes a really long time
; (check-equal? (day01-part2) 69285)
)