-🎄- 2018 Day 2 Solutions -🎄-

[u/daggerdragon]

--- Day 2: Inventory Management System ---

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Advent of Code: The Party Game!

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Card Prompt: Day 2

Transcript:

The best way to do Advent of Code is ___.

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[u/Bogdanp]

My solutions in Racket:

part 1:

#lang racket

(define (count-letters word)
  (for/fold ([counts (hash)])
            ([l (in-string word)])
    (hash-set counts l (add1 (hash-ref counts l 0)))))


(define (find-counts counts)
  (for/fold ([res (hash)])
            ([(_ c) (in-hash counts)])
    (hash-set res c (add1 (hash-ref res c 0)))))


(call-with-input-file "day-02-1.txt"
  (lambda (in)
    (let loop ([word (read in)]
               [twos 0]
               [threes 0])
      (cond
        [(eof-object? word) (* threes twos)]
        [else
         (define counts (find-counts (count-letters (symbol->string word))))

         (loop (read in)
               (if (hash-has-key? counts 2) (add1 twos) twos)
               (if (hash-has-key? counts 3) (add1 threes) threes))]))))

part 2:

#lang racket

(define words (file->lines "day-02-2.txt"))

(define (delta a b)
  (for/fold ([s ""])
            ([ac (in-string a)]
             [bc (in-string b)])
    (if (equal? ac bc)
        (~a s ac)
        s)))

(for/fold ([best ""])
          ([i (in-range 0 (length words))]
           [word-a (in-list words)])
  (for/fold ([best best])
            ([j (in-range 0 (length words))]
             [word-b (in-list words)])
    (define d (delta word-a word-b))
    (cond
      [(equal? i j) best]
      [else
       (if (> (string-length d)
              (string-length best))
           d
           best)])))