Day 5.

input/05.txt

@@ -0,0 +1 @@
+3,225,1,225,6,6,1100,1,238,225,104,0,1002,188,27,224,1001,224,-2241,224,4,224,102,8,223,223,1001,224,6,224,1,223,224,223,101,65,153,224,101,-108,224,224,4,224,1002,223,8,223,1001,224,1,224,1,224,223,223,1,158,191,224,101,-113,224,224,4,224,102,8,223,223,1001,224,7,224,1,223,224,223,1001,195,14,224,1001,224,-81,224,4,224,1002,223,8,223,101,3,224,224,1,224,223,223,1102,47,76,225,1102,35,69,224,101,-2415,224,224,4,224,102,8,223,223,101,2,224,224,1,224,223,223,1101,32,38,224,101,-70,224,224,4,224,102,8,223,223,101,3,224,224,1,224,223,223,1102,66,13,225,1102,43,84,225,1101,12,62,225,1102,30,35,225,2,149,101,224,101,-3102,224,224,4,224,102,8,223,223,101,4,224,224,1,223,224,223,1101,76,83,225,1102,51,51,225,1102,67,75,225,102,42,162,224,101,-1470,224,224,4,224,102,8,223,223,101,1,224,224,1,223,224,223,4,223,99,0,0,0,677,0,0,0,0,0,0,0,0,0,0,0,1105,0,99999,1105,227,247,1105,1,99999,1005,227,99999,1005,0,256,1105,1,99999,1106,227,99999,1106,0,265,1105,1,99999,1006,0,99999,1006,227,274,1105,1,99999,1105,1,280,1105,1,99999,1,225,225,225,1101,294,0,0,105,1,0,1105,1,99999,1106,0,300,1105,1,99999,1,225,225,225,1101,314,0,0,106,0,0,1105,1,99999,1108,226,677,224,1002,223,2,223,1005,224,329,101,1,223,223,108,226,226,224,1002,223,2,223,1005,224,344,1001,223,1,223,1107,677,226,224,1002,223,2,223,1006,224,359,101,1,223,223,1008,226,226,224,1002,223,2,223,1005,224,374,101,1,223,223,8,226,677,224,102,2,223,223,1006,224,389,101,1,223,223,7,226,677,224,1002,223,2,223,1005,224,404,1001,223,1,223,7,226,226,224,1002,223,2,223,1005,224,419,101,1,223,223,107,226,677,224,1002,223,2,223,1005,224,434,101,1,223,223,107,226,226,224,1002,223,2,223,1005,224,449,1001,223,1,223,1107,226,677,224,102,2,223,223,1006,224,464,1001,223,1,223,1007,677,226,224,1002,223,2,223,1006,224,479,1001,223,1,223,1107,677,677,224,1002,223,2,223,1005,224,494,101,1,223,223,1108,677,226,224,102,2,223,223,1006,224,509,101,1,223,223,7,677,226,224,1002,223,2,223,1005,224,524,1001,223,1,223,1008,677,226,224,102,2,223,223,1005,224,539,1001,223,1,223,1108,226,226,224,102,2,223,223,1005,224,554,101,1,223,223,107,677,677,224,102,2,223,223,1006,224,569,1001,223,1,223,1007,226,226,224,102,2,223,223,1006,224,584,101,1,223,223,8,677,677,224,102,2,223,223,1005,224,599,1001,223,1,223,108,677,677,224,1002,223,2,223,1005,224,614,101,1,223,223,108,226,677,224,102,2,223,223,1005,224,629,101,1,223,223,8,677,226,224,102,2,223,223,1006,224,644,1001,223,1,223,1007,677,677,224,1002,223,2,223,1006,224,659,1001,223,1,223,1008,677,677,224,1002,223,2,223,1005,224,674,101,1,223,223,4,223,99,226

lib.rkt

@@ -5,7 +5,12 @@
 
 (provide problem-input
          show-solution
-         sum)
+         sum
+         neq?
+         nzero?
+         list-ref*
+         number->digits-reverse
+         number->digits)
 
 ;; IO helpers
 
@@ -26,3 +31,32 @@
 
 ;; sum : (listof number) -> number
 (define (sum ns) (apply + ns))
+
+;; neq : any -> any -> boolean
+(define (neq? v1 v2)
+  (not (eq? v1 v2)))
+
+;; nzero? : number -> boolean
+(define (nzero? n)
+  (not (zero? n)))
+
+;; list-ref* : (listof any) -> number -> any -> any
+;; Same as list-ref, except a default value is provided
+;; if the index is beyond the length of the list.
+(define (list-ref* lst pos failure-result)
+  (if (>= pos (length lst))
+      failure-result
+      (list-ref lst pos)))
+
+;; number->digits-reverse : number -> (listof number)
+;; Return the digits of the given number in reverse order (i.e. RTL)
+(define (number->digits-reverse n)
+  (if (< n 10)
+      (list n)
+      (cons (remainder n 10)
+            (number->digits-reverse (quotient n 10)))))
+
+;; number->digits : number -> (listof number)
+;; Return the digits of the given number (LTR)
+(define (number->digits n)
+  (reverse (number->digits-reverse n)))

src/05.rkt

@@ -0,0 +1,98 @@
+#lang racket
+
+(require "../lib.rkt")
+
+;; string->program : string -> (listof number)
+;; A program is a list of numbers,
+;; which are sequences of instructions and parameters.
+(define (string->program str)
+  (map string->number (string-split str ",")))
+
+(define input
+  (string->program (car (problem-input 5))))
+
+(struct instruction
+  (opcode mode1 mode2 mode3)
+  #:transparent)
+
+;; fetch : number -> number -> program -> program
+;; If the mode is 0, the value at pointer is an address.
+;; If the mode is 1, the value at pointer is immediate.
+;; Return the value at that address or the immediate.
+(define (fetch mode pointer program)
+  (if (zero? mode)
+      (list-ref program (list-ref program pointer))
+      (list-ref program pointer)))
+
+;; write : number -> number -> program -> program
+;; Write the value into the location at pointer.
+(define (write value pointer program)
+  (list-set program (list-ref program pointer) value))
+
+;; decode-instr : number -> instruction
+;; An encoded instruction is anywhere from 1 to 4 digits long.
+;; The last one or two digits represent the opcode, which can be:
+;;   - 1/2: add/multiply parameters 1 and 2 and store in parameter 3
+;;   - 3:   take an input and store in parameter 1
+;;   - 4:   output parameter 1
+;;   - 5/6: if parameter 1 is non-zero/zero, jump to parameter 2
+;;   - 7/8: if parameter 1 is less-than/equal-to parameter 2,
+;;          store 1 else store 0 in parameter 3
+;;   - 99:  halt
+;; The next few digits to the left of the opcode (if any) represent
+;; the mode of each parameter, with that of parameter i in the digit
+;; i digits to the left of the opcode.
+;; Note that leading zeroes in the encoded instruction are omitted.
+(define (decode-instr n)
+  (let* ([cs (number->digits-reverse n)]
+         [ops '(1 2 3 4 5 6 7 8 99)]
+         [op? (λ (v) (member v ops))])
+    (match cs
+      [(list-rest (? op? op) rest)
+       (instruction op
+                    (list-ref* rest 1 0)
+                    (list-ref* rest 2 0)
+                    (list-ref* rest 3 0))]
+      [(list-rest 9 9 _)
+       (instruction 99 0 0 0)])))
+
+;; exec : number -> program -> program
+(define (exec pointer program)
+  (let* ([instr (decode-instr (list-ref program pointer))]
+         [v1 (λ () (fetch (instruction-mode1 instr) (+ pointer 1) program))]
+         [v2 (λ () (fetch (instruction-mode2 instr) (+ pointer 2) program))]
+         [next-pointer
+          (λ (op) (match op
+                    [(or 1 2 7 8) (+ pointer 4)]
+                    [(or 3 4) (+ pointer 2)]
+                    [(or 5 6) (+ pointer 3)]))]
+         [arith
+          (λ (op) (match op [1 +] [2 *]))]
+         [jump-if
+          (λ (op) (match op [5 nzero?] [6 zero?]))]
+         [lt-eq
+          (λ (op) (match op [7 <] [8 =]))])
+    (match (instruction-opcode instr)
+      [(and op (or 1 2))
+       (let* ([program (write ((arith op) (v1) (v2)) (+ pointer 3) program)])
+         (exec (next-pointer op) program))]
+      [3
+       (let* ([input (read)]
+              [program (write input (+ pointer 1) program)])
+         (exec (next-pointer 3) program))]
+      [4
+       (displayln (v1))
+       (exec (next-pointer 4) program)]
+      [(and op (or 5 6))
+       (let* ([pointer (if ((jump-if op) (v1)) (v2)
+                           (next-pointer op))])
+         (exec pointer program))]
+      [(and op (or 7 8))
+       (let* ([v3 (if ((lt-eq op) (v1) (v2)) 1 0)]
+              [program (write v3 (+ pointer 3) program)])
+         (exec (next-pointer op) program))]
+      [99 program])))
+
+(define (execute)
+  (exec 0 input)
+  (void))