days 1–4

2020/01.rkt

@@ -0,0 +1,10 @@
+#lang br
+(require racket/file rackunit)
+
+(define (solve combo-length)
+  (for/first ([c (in-combinations (map string->number (file->lines "01.rktd")) combo-length)]
+            #:when (eq? 2020 (apply + c)))
+  (apply * c)))
+
+(check-equal? (solve 2) 1007331)
+(check-equal? (solve 3) 48914340)

2020/01.rktd

@@ -0,0 +1,200 @@
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2020/02.rkt

@@ -0,0 +1,21 @@
+#lang br
+(require racket/file rackunit)
+
+(struct rec (password target low high))
+(define recs (for/list ([ln (file->lines "02.rktd")])
+               (match-define (list range target password) (string-split ln))
+               (match-define (list low high) (map string->number (string-split range "-")))
+               (rec password (string-ref (string-trim target ":") 0) low high)))
+               
+(check-equal?
+ (for/sum ([rec recs])
+   (define howmany (count (λ (c) (char=? c (rec-target rec))) (string->list (rec-password rec))))
+   (if (<= (rec-low rec) howmany (rec-high rec)) 1 0))
+ 422)
+
+(check-equal?
+ (for/sum ([rec recs])
+   (define low? (char=? (rec-target rec) (string-ref (rec-password rec) (sub1 (rec-low rec)))))
+   (define high? (char=? (rec-target rec) (string-ref (rec-password rec) (sub1 (rec-high rec)))))
+   (if (or (and low? (not high?)) (and high? (not low?))) 1 0))
+ 451)

2020/03.rkt

@@ -0,0 +1,20 @@
+#lang br
+(require racket/file rackunit)
+
+(define (trees-in-slope horiz vert)
+  (for/fold ([mod 0]
+             [sum 0]
+             #:result sum)
+            ([(ln lidx) (in-indexed (file->lines "03.rktd"))]
+             #:when (zero? (modulo lidx vert)))
+    (values (+ mod horiz)
+            (if (char=? #\# (string-ref ln (modulo mod (string-length ln)))) (add1 sum) sum))))
+
+(check-equal? (trees-in-slope 3 1) 151)
+
+(check-equal? (apply * (list
+                        (trees-in-slope 1 1)
+                        (trees-in-slope 3 1)
+                        (trees-in-slope 5 1)
+                        (trees-in-slope 7 1)
+                        (trees-in-slope 1 2))) 7540141059)

2020/03.rktd

@@ -0,0 +1,323 @@
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2020/04.rkt

@@ -0,0 +1,35 @@
+#lang br
+(require racket/file rackunit)
+
+(define passports (for/list ([pstr (string-split (file->string "04.rktd") #rx"\n\n+")])
+                    (for/hash ([kvstr (string-split pstr)])
+                      (apply values (string-split kvstr ":")))))
+
+(define required-fields '("byr" "iyr" "eyr" "hgt" "hcl" "ecl" "pid")) ; "cid" is not required
+
+(define (passport-keys-valid? p)
+  (for*/and ([passport-keys (in-value (hash-keys p))]
+            [field required-fields])
+    (member field passport-keys)))
+
+(check-equal? (count passport-keys-valid? passports) 202)
+
+(define (stringval-in-range str low high)
+  (<= low (string->number str) high))
+
+(define (passport-values-valid? p)
+  (and
+   (stringval-in-range (hash-ref p "byr") 1920 2002)
+   (stringval-in-range (hash-ref p "iyr") 2010 2020)
+   (stringval-in-range (hash-ref p "eyr") 2020 2030)
+   (let ([hgt (hash-ref p "hgt")])
+     (cond
+       [(string-suffix? hgt "cm") (stringval-in-range (string-trim hgt "cm") 150 193)]
+       [(string-suffix? hgt "in") (stringval-in-range (string-trim hgt "in") 59 76)]
+       [else #false]))
+   (let ([hcl (hash-ref p "hcl")])
+     (and (regexp-match #rx"#......" hcl) (string->number (string-trim hcl "#") 16)))
+   (member (hash-ref p "ecl") '("amb" "blu" "brn" "gry" "grn" "hzl" "oth"))
+   (let ([pid (hash-ref p "pid")]) (and (= 9 (string-length pid)) (string->number pid)))))
+
+(check-equal? (count (λ (p) (and (passport-keys-valid? p) (passport-values-valid? p))) passports) 137)