Micah Cantor
@micahcantor.bsky.social
Software engineer @ Rinse • Grinnell College '24 • Washington, DC
https://micahcantor.com
https://micahcantor.com
I'm a little behind now, but here's day 4! #AdventOfCode
December 21, 2024 at 7:26 PM
I'm a little behind now, but here's day 4! #AdventOfCode
December 3, 2024 at 3:30 AM
![#lang racket/base
(require racket/port)
(require racket/string)
(require racket/list)
(require racket/hash)
(define (parse filename)
(define lines (port->lines (open-input-file filename) #:close? #t))
(define input-pairs
(for/list ([line lines])
(map string->number (string-split line " "))))
(define left (map car input-pairs))
(define right (map cadr input-pairs))
(values left right))
(define (solve-part-1 left right)
(define left-sorted (sort left <=))
(define right-sorted (sort right <=))
(apply + (map abs (map - left-sorted right-sorted))))
(define (solve-part-2 left right)
(define right-appearances (make-hash))
(for ([x right])
(hash-update! right-appearances x add1 0))
(define similarity-scores
(for/list ([x left])
(* x (hash-ref right-appearances x 0))))
(apply + similarity-scores))
(define-values (left right) (parse "input.txt"))
(solve-part-1 left right)
(solve-part-2 left right)](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:v7oqpn7itgfqmm7ccvqwutjl/bafkreiarcgh7p4qjlh4qx57zev7npgfcxt4sryrseyh6jftulqdwmmrl4a@jpeg)