Refactored IntCode to internally use a hashmap instead of a vector.

lib.rkt

@@ -12,7 +12,7 @@
 
          make-vector-grid
          vectors->lists
-         hash->vector
+         hash->vectors
          show-list-grid
          show-vector-grid
          show-hash-grid
@@ -38,7 +38,9 @@
          list->queue
 
          vector-ref*
-         vector-set!*)
+         vector-set!*
+         hash->vector
+         vector->hash)
 
 
 ;; Function helpers ;;
@@ -60,7 +62,7 @@
          [path     (string-append "../input/" filename ".txt")])
     (read-lines path)))
 
-;; show-solution : any/c -> any/c -> void
+;; show-solution : a -> b -> void
 ;; Print part1 and part2 on separate lines.
 (define (show-solution part1 part2)
   (printf "Part 1: ~a\nPart 2: ~a\n" part1 part2))
@@ -80,10 +82,10 @@
 (define (vectors->lists vector-grid)
   (map vector->list (vector->list vector-grid)))
 
-;; hash->vector : hash-grid -> number -> vector-grid
+;; hash->vectors : hash-grid -> number -> vector-grid
 ;; Where the position is not in the hash-grid,
 ;; the vector-grid takes on the default value.
-(define (hash->vector hash-grid [default 0])
+(define (hash->vectors hash-grid [default 0])
   (let* ([keys (hash-keys hash-grid)]
          [xs (map car keys)]
          [ys (map cdr keys)]
@@ -113,7 +115,7 @@
 
 ;; show-hash-grid : (hashof (value => char)) -> hash-grid -> number -> void
 (define (show-hash-grid char-hash hash-grid [default 0])
-  (show-vector-grid char-hash (hash->vector hash-grid default)))
+  (show-vector-grid char-hash (hash->vectors hash-grid default)))
 
 
 ;; Number helpers ;;
@@ -189,7 +191,7 @@
             (cons (f v (first lst)) lst))
           (list init) lst)))
 
-;; list-ref* : (listof any) -> number -> any -> any
+;; list-ref* : (listof a) -> number -> a -> a
 ;; 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)
@@ -224,7 +226,7 @@
          [lists (map (λ (lst) (take lst min-len)) lists)])
     (apply map list lists)))
 
-;; list->queue : (listof any) -> (queueof any)
+;; list->queue : (listof a) -> (queueof a)
 ;; Creates a queue and adds elements of list in order
 (define (list->queue lst)
   (let ([Q (make-queue)])
@@ -251,4 +253,16 @@
   (let ([new-vec (make-vector (max (vector-length vec) (add1 pos)))])
     (vector-copy! new-vec 0 vec)
     (vector-set! new-vec pos v)
-    new-vec))
+    new-vec))
+
+;; hash->vector : (hashof (number => a)) -> (vectorof a)
+;; Convert an intmap into a mutable vector
+(define (hash->vector hash [default 0])
+  (let ([length (add1 (apply max (hash-keys hash)))])
+    (build-vector length (λ (i) (hash-ref hash i default)))))
+
+;; vector->hash : (vectorof a) -> (hashof (number => a))
+;; Convert a vector into an immutable intmap
+(define (vector->hash vec)
+  (let ([kvs (map cons (range (vector-length vec)) (vector->list vec))])
+    (make-immutable-hash kvs)))

src/IntCode.rkt

@@ -3,17 +3,17 @@
 (require racket/vector
          "../lib.rkt")
 
-(define (vector-ref vec pos)
-  (vector-ref* vec pos 0))
-
-;; string->program : string -> (listof number)
+;; string->program : string -> (vectorof number)
 ;; A program is a list of numbers,
 ;; which are sequences of instructions and parameters.
 (define (string->program str)
   (list->vector (map string->number (string-split str ","))))
 
+(define (hash-ref* hash key)
+  (hash-ref hash key 0))
+
 (define (program? p)
-  (vectorof number?))
+  hash?)
 
 ;; state =
 ;;       | out number (() -> state)
@@ -38,21 +38,21 @@
     [in (resume) (resume input)]
     [else (error "resume-with-input: Unexpected program state.")]))
 
-;; resume-with-io : state -> (listof number) -> (listof number)
+;; resume-with-io : state -> (listof number) -> (listof number) -> (listof number)
 ;; Run the program, providing input as needed, and collecting output.
-(define (resume-with-io st inputs)
+(define (resume-with-io st inputs [outputs '()])
   (type-case state st
     [in (resume)
-        (resume-with-io (resume (car inputs)) (cdr inputs))]
+        (resume-with-io (resume (car inputs)) (cdr inputs) outputs)]
     [out (value resume)
-         (cons value (resume-with-io (resume) inputs))]
-    [halt (program) '()]))
+         (resume-with-io (resume) inputs (cons value outputs))]
+    [halt (program) (reverse outputs)]))
 
-;; halt-with-program : state -> program
+;; halt-with-program : state -> (vectorof number)
 ;; Return program state of halted execution.
 (define (halt-with-program st)
   (type-case state st
-    [halt (program) program]
+    [halt (program) (hash->vector program)]
     [else (error "halt-with-program: Unexpected program state.")]))
 
 ;; exec* : program -> number -> number -> state
@@ -74,7 +74,7 @@
 ;; If the mode is 2, the value at pointer is an address to be offset by base.
 ;; Note that leading zeroes in the encoded instruction are omitted.
 (define (exec* program #:ptr [pointer 0] #:base [base 0])
-  (define instruction (vector-ref program pointer))
+  (define instruction (hash-ref* program pointer))
   (define opcode (remainder instruction 100))
   (define next-pointer
     (match opcode
@@ -84,9 +84,9 @@
       [99 (+ pointer 1)]))
   (define (get-location index mode)
     (match mode
-      [0 (vector-ref program (+ pointer index))]
+      [0 (hash-ref* program (+ pointer index))]
       [1 (+ pointer index)]
-      [2 (+ (vector-ref program (+ pointer index)) base)]))
+      [2 (+ (hash-ref* program (+ pointer index)) base)]))
   (let* ([mode1 (remainder (quotient instruction 100) 10)]
          [mode2 (remainder (quotient instruction 1000) 10)]
          [mode3 (remainder (quotient instruction 10000) 10)]
@@ -95,19 +95,19 @@
          [l2 (λ () (get-location 2 mode2))]
          [l3 (λ () (get-location 3 mode3))]
          ;; v* : call to read values from program
-         [v1 (λ () (vector-ref program (l1)))]
-         [v2 (λ () (vector-ref program (l2)))]
-         [v3 (λ () (vector-ref program (l3)))])
+         [v1 (λ () (hash-ref* program (l1)))]
+         [v2 (λ () (hash-ref* program (l2)))]
+         [v3 (λ () (hash-ref* program (l3)))])
     (match opcode
       [(or 1 2)
        (let* ([arith (match opcode [1 +] [2 *])]
               [value (arith (v1) (v2))]
-              [program (vector-set!* program (l3) value)])
+              [program (hash-set program (l3) value)])
          (exec* program #:ptr next-pointer #:base base))]
       [3
        (let* ([resume
                (λ (input)
-                 (let ([program (vector-set!* program (l1) input)])
+                 (let ([program (hash-set program (l1) input)])
                    (exec* program #:ptr next-pointer #:base base)))])
          (in resume))]
       [4
@@ -122,7 +122,7 @@
       [(or 7 8)
        (let* ([lt-eq (match opcode [7 <] [8 =])]
               [value (if (lt-eq (v1) (v2)) 1 0)]
-              [program (vector-set!* program (l3) value)])
+              [program (hash-set program (l3) value)])
          (exec* program #:ptr next-pointer #:base base))]
       [9
        (let ([base (+ base (v1))])
@@ -130,6 +130,9 @@
       [99
        (halt program)])))
 
-;; Just so we always run the program on a fresh copy
+;; The external interface accepts a vector,
+;; while the internals use an immutable hashmap
+;; for functional purity and performance
 (define (exec program #:ptr [pointer 0] #:base [base 0])
-  (exec* (vector-copy program) #:ptr pointer #:base base))
+  (let* ([hash-program (vector->hash program)])
+    (exec* hash-program #:ptr pointer #:base base)))