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1 files changed, 33 insertions, 0 deletions

diff --git a/racket/aoc2020/day-02/day-02.rkt b/racket/aoc2020/day-02/day-02.rkt
new file mode 100644
index 0000000..9e22a1a
--- /dev/null
+++ b/racket/aoc2020/day-02/day-02.rkt
@@ -0,0 +1,33 @@
+#lang racket
+(require "../../jj-aoc.rkt"
+         threading)
+
+(struct policy (least most char pwd) #:transparent)
+
+(define (make-policy least-str most-str char-str pwd)
+  (policy (string->number least-str) (string->number most-str) (string-ref char-str 0) pwd))
+
+(define policies
+  (for/list ([l (in-lines (open-day 02 2020))])
+    (~>> l (regexp-match #px"(\\d+)-(\\d+) (\\w): (.*)") rest (apply make-policy))))
+
+;; part 1
+(define (valid-policy? p)
+  (~>> p
+       policy-pwd
+       string->list
+       (count (curry char=? (policy-char p)))
+       ((λ (n) (and (>= n (policy-least p)) (<= n (policy-most p)))))))
+
+(for/sum ([p (in-list policies)] #:when (valid-policy? p)) 1)
+
+;; part 2
+(define (valid-revised-policy? p)
+  (~>> p
+       policy-pwd
+       string->list
+       ((λ (lst) (list (list-ref lst (sub1 (policy-most p))) (list-ref lst (sub1 (policy-least p))))))
+       (count (curry char=? (policy-char p)))
+       (= 1)))
+
+(for/sum ([p (in-list policies)] #:when (valid-revised-policy? p)) 1)