Two sum: Difference between revisions

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@@ Line 314: / Line 314: @@
 ====Returning all matches====
-Using sequence (for a cartesian product) and nubBy, and listing multiple solutions when they exist:
+Listing multiple solutions when they exist:
-<lang haskell>import Data.List (elem, elemIndices, nubBy)
+<lang haskell>sumTo :: Int -> [Int] -> [(Int, Int)]
+sumTo n ns =
+  let ixs = zip [0 ..] ns
-summingPairIndices :: Int -> [Int] -> [[Int]]
+  in ixs >>=
-summingPairIndices n xs =
-  (>>= (`elemIndices` xs)) <$>
+     (\(i, x) ->
+         ixs >>=
-  nubBy
-    (\xy zs -> and ((`elem` zs) <$> xy))
+         \(j, y) ->
-    (sequence [xs, xs] >>=
+            [ (i, j)
-     (\[x, y] ->
+            | (i < j) && (x + y) == n ])
-         [ [x, y]
-         | x /= y && x + y == n ]))
 main :: IO ()
-main = print $ summingPairIndices 21 [0, 2, 11, 19, 90, 10]</lang>
+main = print $ sumTo 21 [0, 2, 11, 19, 90, 10]</lang>
 {{Out}}
-<pre>[[1,3],[2,5]]</pre>
+<pre>[(1,3),(2,5)]</pre>
 =={{header|Icon}} and {{header|Unicon}}==