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adventofcode
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Day 06: Move assocf into library.

This commit is contained in:
Jonathan Chan 2021-12-05 22:11:14 -08:00 committed by Jonathan Chan
parent cbbd3b60fe
commit 4f9e8ea253
2 changed files with 9 additions and 4 deletions
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11
lib.rkt
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@ -188,7 +188,7 @@
(cons (f v (first lst)) lst)) (cons (f v (first lst)) lst))
(list init) lst))) (list init) lst)))
;; list-ref* : (listof a) -> number -> a -> (or a #f) ;; list-ref* : (listof a) -> number -> a -> (or/c a #f)
;; Same as list-ref, except a default value is provided ;; Same as list-ref, except a default value is provided
;; if the index is beyond the length of the list. ;; if the index is beyond the length of the list.
(define (list-ref* lst pos [failure-result #f]) (define (list-ref* lst pos [failure-result #f])
@ -196,13 +196,20 @@
failure-result failure-result
(list-ref lst pos))) (list-ref lst pos)))
;; first* : (listof a) -> (or a #f) ;; first* : (listof a) -> (or/c a #f)
;; Get first of list or default if empty ;; Get first of list or default if empty
(define (first* lst [failure-result #f]) (define (first* lst [failure-result #f])
(match lst (match lst
['() failure-result] ['() failure-result]
[`(,hd ,@_) hd])) [`(,hd ,@_) hd]))
;; assocf : a -> (listof (cons a b)) -> (or/c b #f)
;; Returns cdr if assoc succeeds, otherwise #f
(define (assocf a lst)
(match (assoc a lst)
[`(,_ . ,b) b]
[else #f]))
;; repeat : number -> (listof any) -> (listof any) ;; repeat : number -> (listof any) -> (listof any)
(define (repeat m lst) (define (repeat m lst)
(if (zero? m) '() (if (zero? m) '()

2
src/06.rkt
View File

@ -8,8 +8,6 @@
string-csv string-csv
(map string->number _))) (map string->number _)))
(define assocf (∘ cdr assoc))
(define fish (define fish
(for/list ([age (range 0 9)]) (for/list ([age (range 0 9)])
(cons age (count #{= % age} input)))) (cons age (count #{= % age} input))))