From 5eb58ad076f2cd435b11b140820da224b60b73d5 Mon Sep 17 00:00:00 2001 From: Aria Date: Mon, 2 Jan 2023 21:58:56 +0000 Subject: initial commit --- 2021/day3/03b.rkt | 35 +++++++++++++++++++++++++++++++++++ 1 file changed, 35 insertions(+) create mode 100644 2021/day3/03b.rkt (limited to '2021/day3/03b.rkt') diff --git a/2021/day3/03b.rkt b/2021/day3/03b.rkt new file mode 100644 index 0000000..aea9c86 --- /dev/null +++ b/2021/day3/03b.rkt @@ -0,0 +1,35 @@ +#lang racket + +(define (mode xs) + (define ht (make-hash)) + (define max-key '0) + (for ([x xs]) + (define new-val (+ 1 (hash-ref ht x 0))) + (hash-set! ht x new-val) + (if (> new-val (hash-ref ht max-key 0)) (set! max-key x) 3)) + (cond [(= (hash-ref ht #\0 0) (hash-ref ht #\1 0)) #f] + [else max-key])) + +(define (flip x) + (cond [(char=? x #\0) #\1] + [else #\0])) + +(define (bit-criteria lines least [fallback (cond [least #\0] [else #\1])] [n 0]) + (cond [(= (length lines) 1) (car lines)] + [else + (define bits (map (curryr string-ref n) lines)) + (define bMode (mode bits)) + (define criteria (cond [(not bMode) fallback] + [least (flip bMode)] + [else bMode])) + (bit-criteria (filter (lambda (x) (char=? criteria (string-ref x n))) + lines) + least fallback (+ n 1))])) + +(define input (open-input-file "input")) +(define lines (port->lines input)) + +(define oxy (string->number (bit-criteria lines #f) 2)) +(define co2 (string->number (bit-criteria lines #t) 2)) + +(* oxy co2) -- cgit v1.2.3