praxis

commit 895c2c80df9f3152ea361670da82b6e8a0b51934
parent f86fa28d6caff89f884b300fd39ab74021e53408
Author: Jared Tobin <jared@jtobin.ca>
Date:   Mon, 11 Jan 2016 19:48:27 +1300

2015/12/18.

Diffstat:
A
20151218_repeated/Foo.hs
 | 
34
++++++++++++++++++++++++++++++++++

1 file changed, 34 insertions(+), 0 deletions(-)
diff --git a/20151218_repeated/Foo.hs b/20151218_repeated/Foo.hs
@@ -0,0 +1,34 @@
+-- First, find the first non-repeated element in an unsorted array. For
+-- instance, in the array [3, 5, 3, 2, 1], element 3 is repeated, elements 5,
+-- 2, and 1 are non-repeated, and the first of those is 5. Second, find the
+-- first element that appears an even number of times in an unsorted array. For
+-- instance, in the array [5, 3, 5, 1, 5, 1, 3], elements 1 and 3 appear an
+-- even number of times, and the first of those is 3.
+
+import Data.Function
+import Data.List
+import qualified Data.Map.Strict as MS
+import qualified Data.Set as S
+
+one :: Ord a => [a] -> a
+one =
+    snd
+  . minimumBy (compare `on` fst)
+  . concat
+  . filter ((< 2) . length)
+  . groupBy ((==) `on` snd)
+  . sortBy (compare `on` snd) . zip [1..]
+
+two :: Ord a => [a] -> a
+two =
+    snd
+  . minimumBy (compare `on` fst)
+  . concat
+  . filter (even . length)
+  . groupBy ((==) `on` snd)
+  . sortBy (compare `on` snd) . zip [1..]
+
+test0 = [3, 5, 3, 2, 1]
+test1 = [5, 3, 5, 1, 5, 1, 3]
+
+