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1 files changed, 32 insertions, 0 deletions

diff --git a/racket/aoc2023/day-06/day-06.rkt b/racket/aoc2023/day-06/day-06.rkt
new file mode 100644
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--- /dev/null
+++ b/racket/aoc2023/day-06/day-06.rkt
@@ -0,0 +1,32 @@
+#lang racket
+
+(require advent-of-code
+         threading)
+
+(match-define (list times distances)
+  (~> (open-aoc-input (find-session) 2023 6 #:cache #true) port->lines))
+
+;; part 1
+(define get-numbers (λ~> string-split (map string->number _) rest))
+(define (find-bound race-time dist button-time step)
+  (if (< dist (* button-time (- race-time button-time)))
+      button-time
+      (find-bound race-time dist (+ step button-time) step)))
+
+(define (lower-bound rtime dist)
+  (find-bound rtime dist 1 1))
+(define (upper-bound rtime dist)
+  (find-bound rtime dist rtime -1))
+
+(for/fold ([acc 1])
+          ([race-time (in-list (get-numbers times))]
+           [distance (in-list (get-numbers distances))])
+  (* acc (add1 (- (upper-bound race-time distance) (lower-bound race-time distance)))))
+
+;; part 2
+
+(define unkern (λ~>> get-numbers (apply ~a) string->number))
+(define big-time (unkern times))
+(define big-distance (unkern distances))
+
+(add1 (- (upper-bound big-time big-distance) (lower-bound big-time big-distance)))