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