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1 files changed, 24 insertions, 0 deletions

diff --git a/racket/leetcode/lc-989-add-to-array-form.rkt b/racket/leetcode/lc-989-add-to-array-form.rkt
new file mode 100644
index 0000000..c88bdc9
--- /dev/null
+++ b/racket/leetcode/lc-989-add-to-array-form.rkt
@@ -0,0 +1,24 @@
+#lang racket
+(define/contract (add-to-array-form num k)
+  (-> (listof exact-integer?) exact-integer? (listof exact-integer?))
+  (define rev-num (reverse num))
+  (define raw-array-form
+    (cond [(= k 0) num]
+          [else
+           (for/fold ([sum-list '()]
+                      [addend k]
+                      [carry 0]
+                      #:result sum-list)
+                     ([place (append rev-num
+                                     (make-list (add1 (order-of-magnitude k)) 0))])
+             (let* ([place-sum (+ place carry (modulo addend 10))]
+                    [to-carry (quotient place-sum 10)]
+                    [new-place (modulo place-sum 10)])
+               (values (cons new-place sum-list)
+                       (quotient addend 10)
+                       to-carry)))]))
+  (match-define-values
+    (result _) (drop-common-prefix raw-array-form
+                                   (make-list (length raw-array-form) 0)))
+  (cond [(empty? result) '(0)]
+        [else result]))
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