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1 files changed, 24 insertions, 0 deletions

diff --git a/racket/leetcode/lc-645-set-mismatch.rkt b/racket/leetcode/lc-645-set-mismatch.rkt
new file mode 100644
index 0000000..a9d9a61
--- /dev/null
+++ b/racket/leetcode/lc-645-set-mismatch.rkt
@@ -0,0 +1,24 @@
+#lang racket
+
+(define/contract (find-error-nums nums)
+  (-> (listof exact-integer?) (listof exact-integer?))
+  (define nums-set (list->set nums))
+  (define range-set (apply set (range 1 (+ 2 (set-count nums-set)))))
+  (define missing-num (first (set->list (set-subtract range-set nums-set))))
+  (define necessary-num
+    (if (set-member? nums-set (- missing-num 1))
+        (+ missing-num 1)
+        (- missing-num 1)))
+  (list missing-num necessary-num))
+
+(find-error-nums '(1 2 2 4))
+
+(define fact-stream
+  (letrec ([f (lambda (x y)
+                (cond
+                  [(zero? (modulo (- y 1) 3)) (cons (* 3 x) (lambda() (f (* x
+                                                                            y) (+ y 1))))]
+                  [else (cons x (lambda() (f (* x y) (+ y 1))))])
+                [else (cons x (lambda() (f (* x y) (+ y 1))))]
+                (lambda () (f 1 2))
+                )])))
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