Merge branch 'main' of https://github.com/hunkyjimpjorps/AdventOfCode

1 files changed, 44 insertions, 0 deletions

diff --git a/2020/day-05/day-05.rkt b/2020/day-05/day-05.rkt
new file mode 100644
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--- /dev/null
+++ b/2020/day-05/day-05.rkt
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+#lang racket
+(require "../../jj-aoc.rkt"
+         threading
+         algorithms)
+
+(define tickets
+  (for/list
+      ([l (in-lines (open-day 5 2020))])
+    (~>> l
+         (regexp-match #px"(.{7})(.{3})" )
+         rest)))
+
+(define (find-place str min-p max-p l r)
+  (if (string=? "" str)
+      min-p
+      (let ([p-range (/ (add1 (- max-p min-p)) 2)]
+            [c (substring str 0 1)])
+        (cond
+          [(string=? c l)
+           (find-place (substring str 1) min-p (- max-p p-range) l r)]
+          [(string=? c r)
+           (find-place (substring str 1) (+ min-p p-range) max-p l r)]))))
+
+(define (find-row str) (find-place str 0 127 "F" "B"))
+(define (find-col str) (find-place str 0 7 "L" "R"))
+
+(define (ticket-id t)
+  (let ([row (find-row (first t))]
+        [col (find-col (second t))])
+    (+ col (* 8 row))))
+
+;; part 1
+(define occupied-seats
+  (~>> (for/list ([t (in-list tickets)]) (ticket-id t))))
+
+(apply max occupied-seats)
+
+;; part 2
+(set-first
+ (set-subtract (list->set (inclusive-range (apply min occupied-seats)
+                                           (apply max occupied-seats)))
+               (list->set occupied-seats)))
+
+