diff --git a/src/interviewing.io/2023-09-16-question1.hs b/src/interviewing.io/2023-09-16-question1.hs
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+import qualified Data.List  as List
+import qualified Data.Maybe as Maybe
+import           Data.Set   (Set)
+import qualified Data.Set   as Set
+
+{-
+interviewing.io question:
+<https://interviewing.io/mocks/linked-in-python-matching-pairs>
+
+Given a list of whole positive numbers, how would you go about finding two numbers in that list that sum up to a given target number. Assume no duplicates in list.
+
+-}
+
+
+wholePositiveNumbers :: Set Integer
+wholePositiveNumbers = Set.fromAscList [1..1_000_000]
+
+-- findTargetSumIn xs n =
+--   (if abs (x-n) `member` xs
+--     && abs (x-n) + x == n
+--     then Just (abs (x-n), x)
+--     else Nothing) : findTargetSumIn xs n
+--     where
+--       x =
+ans lst sum = List.nubBy isMirror $ Maybe.catMaybes $ Set.elems $ Set.map (\x ->
+    let x' = abs (x-sum)
+    in
+      if x' `Set.member` lst
+      && x' + x == sum
+        then Just (x',x)
+        else Nothing
+  ) lst
+
+isMirror (a,a') (b,b')
+   = a == b'
+  && b == a'
+
+example  = Set.fromList [14,13,6,7,8,10,1,2]
+example' = Set.fromList [14,13,6,7,8,10,1]
+example'' = Set.fromList [1,14,13,3,6,7,2,8,10,4]
+
+main = do
+  print "Quick 3 answers:"
+  print $ ans example 3
+  print $ ans example' 3
+  print $ ans example'' 5
+
+  print "Long answer"
+  print $ ans wholePositiveNumbers 3