adding old leetcode solutions

1 files changed, 27 insertions, 0 deletions

diff --git a/leetcode/lc-228-summary-ranges.rkt b/leetcode/lc-228-summary-ranges.rkt
new file mode 100644
index 0000000..9140895
--- /dev/null
+++ b/leetcode/lc-228-summary-ranges.rkt
@@ -0,0 +1,27 @@
+#lang racket
+(define (summary-ranges nums)
+  (define range-pairs
+    (cond
+      [(empty? nums) '()]
+      [(empty? (cdr nums)) (list (cons (car nums) (car nums)))]
+      [else (for/fold ([ranges '()]
+                       [open-pair (first nums)]
+                       [prev-num (first nums)]
+                       #:result (append ranges (list (cons open-pair prev-num))))
+                      ([i (cdr nums)])
+              (cond [(= (add1 prev-num) i)
+                     (values ranges
+                             open-pair
+                             i)]
+                    [else
+                     (values (append ranges (list (cons open-pair prev-num)))
+                             i
+                             i)]))]))
+  (for/list ([p (in-list range-pairs)])
+    (cond [(= (car p) (cdr p)) (format "~a" (car p))]
+          [else (format "~a->~a" (car p) (cdr p))])))
+
+(summary-ranges '(0 1 2 4 5 7))
+(summary-ranges '(0 2 3 4 6 8 9))
+(summary-ranges '())
+(summary-ranges '(0))
\ No newline at end of file