Solve 'Basics 08: Find next higher number with same Bits (1's)' kata

src/Kata.hs

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+module Kata (nextHigher) where
+
+-- https://www.codewars.com/kata/56bdd0aec5dc03d7780010a5/train/haskell
+
+nextHigher :: Int -> Int
+nextHigher n = search (n + 1)
+  where
+    bitCountN = bitCount n
+
+    search :: Int -> Int
+    search i
+      | bitCount i == bitCountN = i
+      | otherwise = search (i + 1)
+
+bitCount :: Int -> Int
+bitCount 0 = 0
+bitCount n
+  | rest == 0 = bitCount div2
+  | otherwise = 1 + bitCount div2
+  where
+    (div2, rest) = n `divMod` 2
+
+-- #againwhatlearned
+-- use `popCount` from `Data.Bits` to count the number of bits set to 1 in a number

test/KataSpec.hs

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+module KataSpec (spec) where
+
+import Kata (nextHigher)
+import Test.Hspec
+
+spec :: Spec
+spec = do
+  it "basic tests" $ do
+    nextHigher 128 `shouldBe` 256
+    nextHigher 1 `shouldBe` 2
+    nextHigher 1022 `shouldBe` 1279
+    nextHigher 127 `shouldBe` 191
+    nextHigher 1253343 `shouldBe` 1253359