Two sum: Difference between revisions
Add Haskell
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The numbers with indices 1 and 3 sum to 21
</pre>
=={{header|Haskell}}==
<lang Haskell>
twoSum::(Num a,Ord a) => a -> [a] -> [Int]
twoSum num list = sol ls (reverse ls)
where
ls = zip list [0..]
sol [] _ = []
sol _ [] = []
sol xs@((x,i):us) ys@((y,j):vs) = ans
where
s = x + y
ans | s == num = [i,j]
| j <= i = []
| s < num = sol (dropWhile ((<num).(+y).fst) us) ys
| otherwise = sol xs $ dropWhile ((num <).(+x).fst) vs
main = print $ twoSum 21 [0, 2, 11, 19, 90]
</lang>
{{out}}
<pre>
[1,3]
</pre>
=={{header|Icon}} and {{header|Unicon}}==
{{Trans|Lua}}
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