finish day4, reorg directory

day1.scrbl

@@ -3,7 +3,7 @@
 
 @aoc-title[1]
 
-Our @link-rp["day1/input.txt"]{input} is a string of parentheses that controls an elevator. A left parenthesis @litchar{(} means go up one floor, and a right parenthesis @litchar{)} means go down.
+Our @link-rp["day1-input.txt"]{input} is a string of parentheses that controls an elevator. A left parenthesis @litchar{(} means go up one floor, and a right parenthesis @litchar{)} means go down.
 
 @chunk[<day1>
        <setup>
@@ -110,7 +110,7 @@ The two are similar. The choice comes down to readability and efficiency — me
 
 @chunk[<test>
        (module+ test
-         (define input-str (file->string "input.txt"))
+         (define input-str (file->string "day1-input.txt"))
          (check-equal? (q1 input-str) 74)
          (check-equal? (q1-alt input-str) 74)
          (check-equal? (q2 input-str) 1795)

day2.scrbl

@@ -3,7 +3,7 @@
 
 @aoc-title[2]
 
-Our @link-rp["day2/input.txt"]{input} is a list of strings that represent dimensions of rectangular boxes.
+Our @link-rp["day2-input.txt"]{input} is a list of strings that represent dimensions of rectangular boxes.
 
 @chunk[<day2>
        <setup>
@@ -59,6 +59,6 @@ We take the same approach, with a new @racket[box->ribbon] function.
 
 @chunk[<test>
        (module+ test
-         (define input-str (file->string "input.txt"))
+         (define input-str (file->string "day2-input.txt"))
          (check-equal? (q1 input-str) 1586300)
          (check-equal? (q2 input-str) 3737498))]

day2/daylang.rkt

@@ -1,43 +0,0 @@
-#lang racket
-(require rackunit)
-(provide read-syntax)
-
-(define (get-dimensions str)
-  (map string->number (regexp-match* #px"\\d+" str)))
-
-(define (get-faces dimensions)
-  (define half-faces
-    (for*/list ([first-pos (in-range (sub1 (length dimensions)))]
-                            [second-pos (in-range (add1 first-pos) (length dimensions))])
-                           (list (list-ref dimensions first-pos) (list-ref dimensions second-pos))))
-  (append* (make-list 2 half-faces)))
-
-(define (str->paper str)
-  (define dimensions (get-dimensions str))
-  (define faces (get-faces dimensions))
-  (define areas (map (curry apply *) faces))
-  (define smallest-area (apply min areas))
-  (apply + smallest-area areas))
-
-(define (str->ribbon str)
-  (define dimensions (get-dimensions str))
-  (define faces (get-faces dimensions))
-  (define perimeters (map (λ(face) (* 2 (apply + face))) faces))
-  (define smallest-perimeter (apply min perimeters))
-  (define volume (apply * dimensions))
-  (+ smallest-perimeter volume))
-                 
-(check-equal? (str->paper "2x3x4") 58)
-(check-equal? (str->paper "1x1x10") 43)
-
-(check-equal? (str->ribbon "2x3x4") 34)
-(check-equal? (str->ribbon "1x1x10") 14)
-
-(define (read-syntax source-path-string in-port)
-  (with-syntax ([source-str (string-trim (port->string in-port))]
-                [str->paper str->paper]
-                [str->ribbon str->ribbon])
-    #'(module _ racket
-        (define package-strs (string-split 'source-str))
-        (apply + (map str->paper package-strs))
-        (apply + (map str->ribbon package-strs)))))

day3.scrbl

@@ -3,7 +3,7 @@
 
 @aoc-title[3]
 
-Our @link-rp["day3/input.txt"]{input} is a string made of the characters @litchar{^v<>} that represent north, south, west, and east. Taken together, the string represents a path through an indefinitely large grid.
+Our @link-rp["day3-input.txt"]{input} is a string made of the characters @litchar{^v<>} that represent north, south, west, and east. Taken together, the string represents a path through an indefinitely large grid.
 
 In essence, this a two-dimensional version of the elevator problem in @secref["day-1"].
 
@@ -98,7 +98,7 @@ The solution works the same as before — the only new task is to split the inpu
 
 @chunk[<test>
        (module+ test
-         (define input-str (file->string "input.txt"))
+         (define input-str (file->string "day3-input.txt"))
          (check-equal? (q1 input-str) 2565)
          (check-equal? (q1-complex input-str) 2565)
          (check-equal? (q2 input-str) 2639))]

day3/daylang.rkt

@@ -1,47 +0,0 @@
-#lang racket
-(require rackunit)
-(provide read-syntax)
-
-(define (str->visits str)
-  (define start '(0 0))
-  (define moves (map (λ(move) (case move
-                                [("^") '(0 1)]
-                                [("v") '(0 -1)]
-                                [("<") '(-1 0)]
-                                [(">") '(1 0)]))
-                     (regexp-match* #rx"." str)))
-  (reverse (for/fold ([visit-acc (list start)])
-                     ([move (in-list moves)])
-             (cons (map + move (car visit-acc)) visit-acc))))
-
-(define (str->unique-visits str)
-  (define visits (str->visits str))
-  (length (remove-duplicates visits)))
-
-(define (str->robosanta str)
-  (define-values (reversed-santa-path reversed-robo-path)
-    (for/fold ([santa-acc empty][robo-acc empty])
-              ([c (in-string str)][pos (in-naturals)])
-      (if (even? pos)
-          (values (cons c santa-acc) robo-acc)
-          (values santa-acc (cons c robo-acc)))))
-  (define santa-str (string-append* (map ~a (reverse reversed-santa-path))))
-  (define robo-str (string-append* (map ~a (reverse reversed-robo-path))))
-  (length (remove-duplicates (append (str->visits santa-str) (str->visits robo-str)))))
-
-
-(check-equal? (str->unique-visits ">") 2)
-(check-equal? (str->unique-visits "^>v<") 4)
-
-(check-equal? (str->robosanta "^v") 3)
-(check-equal? (str->robosanta "^>v<") 3)
-(check-equal? (str->robosanta "^v^v^v^v^v") 11)
-
-
-(define (read-syntax source-path-string in-port)
-  (with-syntax ([source-str (string-trim (port->string in-port))]
-                [str->unique-visits str->unique-visits]
-                [str->robosanta str->robosanta])
-    #'(module _ racket
-        (str->unique-visits source-str)
-        (str->robosanta source-str))))

day4-input.txt

@@ -0,0 +1 @@
+iwrupvqb

day4.scrbl

@@ -0,0 +1,51 @@
+#lang scribble/lp2
+@(require scribble/manual aoc-racket/helper)
+@(require (for-label openssl/md5))
+
+@aoc-title[4]
+
+Our @link-rp["day4-input.txt"]{input} is a string of eight characters that represents part of a key for making an MD5 hash.
+
+@chunk[<day4>
+       <setup>
+       <q1>
+       <q2>
+       <test>]
+
+@section{What is the lowest-numbered MD5 hash starting with five zeroes?}
+
+We're asked to create an MD5 hash from an input key that consists of our eight-character input joined to a decimal number. The puzzle asks us to find the lowest decimal number that, when joined to our input, produces an MD5 hash that starts with five zeroes.
+
+Whether or not you already know what an MD5 hash is, you can search the Racket docs and will soon find the @racketmodname[openssl/md5] module and the @racket[md5] function. Then, this puzzle is easy: starting at @racket[0], make new input keys with each integer, and stop when we find one that results in the MD5 hash we want. (The approach is similar to the second part of @secref["day-1"].) 
+
+
+@chunk[<setup>
+       (require racket rackunit openssl/md5)
+       ]
+
+@chunk[<q1>
+       (define (q1 str)
+         (for/or ([i (in-naturals)])
+                 (define md5-key (string-append str (~a i)))
+                 (define md5-hash (md5 (open-input-string md5-key)))
+                 (and (string-prefix? md5-hash "00000") i)))
+       ]
+
+@section{How about six zeroes?}
+
+Exactly the same, except we test for a string of six zeroes. It is likely, however, to take quite a bit longer to run, as the sixth zero essentially makes the criterion 10 times more stringent.
+
+@chunk[<q2>
+       (define (q2 str)
+         (for/or ([i (in-naturals)])
+                 (define md5-key (string-append str (~a i)))
+                 (define md5-hash (md5 (open-input-string md5-key)))
+                 (and (string-prefix? md5-hash "000000") i)))]
+
+@section{Testing our input}
+
+@chunk[<test>
+       (module+ test
+         (define input-str (file->string "day4-input.txt"))
+         (check-equal? (q1 input-str) 346386)
+         (check-equal? (q2 input-str) 9958218))]

helper.rkt

@@ -14,5 +14,5 @@
      (with-syntax ([rp-name (generate-temporary)])
        #'(begin
            (require racket/runtime-path)
-           (define-runtime-path rp-name (expand-user-path where))
+           (define-runtime-path rp-name where)
            @(link (path->string rp-name) text-args ...)))]))

start.scrbl

@@ -9,6 +9,7 @@
 
 @local-table-of-contents[]
 
-@include-section[(submod "day1/main.scrbl" doc)]
+@include-section[(submod "day1.scrbl" doc)]
-@include-section[(submod "day2/main.scrbl" doc)]
+@include-section[(submod "day2.scrbl" doc)]
-@include-section[(submod "day3/main.scrbl" doc)]
+@include-section[(submod "day3.scrbl" doc)]
+@include-section[(submod "day4.scrbl" doc)]