Two sum: Difference between revisions
→{{header|J}}: alternative approach for retrieving indicies
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<lang J>twosum=: ;@{.@(a:,~ ($ <@#: I.@,)@([ = +/~@]))</lang>
'''Alternative approach'''
An alternative method for identifying and returning non-duplicate indicies of the pairs follows.
<lang j> 21 (= +/~) 0 2 11 19 90
0 0 0 0 0
0 0 0 1 0
0 0 0 0 0
0 1 0 0 0
0 0 0 0 0</lang>
The array is symmetrical so we can zero one half to remove duplicate pairs and then retrieve the remaining indicies using sparse array functionality.
<lang j>zeroLowerTri=: * [: </~ i.@#
getIdx=: 4 $. $.
twosum_alt=: getIdx@zeroLowerTri@(= +/~)</lang>
Testing ...
<lang j> 21 twosum_alt 0 2 11 19 90
1 3</lang>
=={{header|Java}}==
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