adding old leetcode solutions

1 files changed, 16 insertions, 0 deletions

diff --git a/leetcode/lc-504-base7.rkt b/leetcode/lc-504-base7.rkt
new file mode 100644
index 0000000..3e75052
--- /dev/null
+++ b/leetcode/lc-504-base7.rkt
@@ -0,0 +1,16 @@
+#lang racket
+
+(define/contract (convert-to-base7 num)
+  (-> exact-integer? string?)
+  (define (max-base-power n base [pow 1])
+    (cond [(n . = . (expt base pow)) pow]
+          [(n . < . (expt base pow)) (sub1 pow)]
+          [else (max-base-power n base (add1 pow))]))
+  (define (add-next-digit n pow acc)
+    (cond [(= pow 0) (string-append acc (number->string n))]
+          [else (add-next-digit (remainder n (expt 7 pow))
+                                (sub1 pow)
+                                (string-append acc
+                                               (number->string (quotient n (expt 7 pow)))))]))
+  (string-append (if (negative? num) "-"  "")
+                 (add-next-digit (abs num) (max-base-power (abs num) 7) "")))
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