104 lines
3.6 KiB
Racket
104 lines
3.6 KiB
Racket
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#lang racket
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(require "../lib.rkt")
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(define input
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(map string->number (string-split (car (problem-input 2)) ",")))
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(define (input-nv nv)
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(append (list (car input) (first nv) (second nv)) (cdddr input)))
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(define (exec pointer program)
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(let* ([opcode (list-ref program pointer)]
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[val1 (list-ref program (list-ref program (+ pointer 1)))]
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[val2 (list-ref program (list-ref program (+ pointer 2)))]
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[val3 (list-ref program (+ pointer 3))]
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[next-program
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(cond [(= opcode 1)
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(list-set program val3 (+ val1 val2))]
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[(= opcode 2)
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(list-set program val3 (* val1 val2))]
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[else program])])
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(if (= opcode 99)
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next-program
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(exec (+ pointer 4) next-program))))
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(define part1
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(car (exec 0 (input-nv '(12 2)))))
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(define part2
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(let* ([nounverbs (cartesian-product (range 100) (range 100))]
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[outputs (map (λ (nv) (car (exec 0 (input-nv nv)))) nounverbs)]
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[nounverb (list-ref nounverbs (index-of outputs 19690720))]
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[noun (first nounverb)]
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[verb (second nounverb)])
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(+ (* 100 noun) verb)))
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(show-solution part1 part2)
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;;;; ALTERNATE SOLUTION
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(define part2-input
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(append (list (car input) 'noun 'verb '(+ noun verb)) (cddddr input)))
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(define (exec-sym pointer program)
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(let* ([opcode (list-ref program pointer)]
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[val1 (list-ref program (list-ref program (+ pointer 1)))]
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[val2 (list-ref program (list-ref program (+ pointer 2)))]
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[val3 (list-ref program (+ pointer 3))]
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[next-program
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(cond [(= opcode 1)
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(list-set program val3 `(+ ,val1 ,val2))]
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[(= opcode 2)
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(list-set program val3 `(* ,val1 ,val2))]
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[else program])])
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(if (= opcode 99)
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next-program
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(exec-sym (+ pointer 4) next-program))))
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(define part2-partial
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(car (exec-sym 4 part2-input)))
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(define (simplify expr)
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(match expr
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; (op n1 n2 e) -> (simplify (op (n1 `op` n2) (simplify e)))
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[(or `(,op (,op ,(? number? n1) ,e) ,(? number? n2))
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`(,op (,op ,e ,(? number? n1)) ,(? number? n2))
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`(,op ,(? number? n1) (,op ,(? number? n2) ,e))
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`(,op ,(? number? n1) (,op ,e ,(? number? n2))))
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(let ([opfun (match op ['+ +] ['* *])])
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(simplify `(,op ,(opfun n1 n2) ,(simplify e))))]
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; (op e1 e2 s) -> (op (simplify (op e1 e2)) s)
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[(or `(,op (,op ,e1 ,(? symbol? s)) ,e2)
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`(,op (,op ,(? symbol? s) ,e1) ,e2)
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`(,op ,e1 (,op ,e2 ,(? symbol? s)))
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`(,op ,e1 (,op ,(? symbol? s) ,e2)))
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`(,op ,(simplify `(,op ,e1 ,e2)) ,s)]
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; (* (+ n1 e) n2) -> (simplify (+ (n1 * n2) (simplify (* n1 e))))
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[(or `(* (+ ,(? number? n2) ,e) ,(? number? n1))
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`(* (+ ,e ,(? number? n2)) ,(? number? n1))
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`(* ,(? number? n1) (+ ,(? number? n2) ,e))
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`(* ,(? number? n1) (+ ,e ,(? number? n2))))
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(simplify `(+ ,(* n1 n2) ,(simplify `(* ,n1 ,e))))]
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[`(* ,(? number? n1) ,(? number? n2)) (* n1 n2)]
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[`(+ ,(? number? n1) ,(? number? n2)) (+ n1 n2)]
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[`(+ ,l ,r) `(+ ,(simplify l) ,(simplify r))]
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[`(* ,l ,r) `(* ,(simplify l) ,(simplify r))]
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[(? number? n) n]
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[(? symbol? s) s]))
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; (+ (+ 520625 (* 270000 noun)) verb) = 19690720
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(define part2-alt
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(let ([simplified (simplify part2-partial)])
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(match simplified
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[`(+ (+ ,n1 (* ,n2 noun)) verb)
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(let* ([dividend (- 19690720 n1)]
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[modulus n2]
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[noun (quotient dividend modulus)]
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[verb (remainder dividend modulus)])
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(+ (* 100 noun) verb))])))
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