In APL, how can I compute the lowest unused positive integer from a given set of integers?
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21-09-2019 - |
Question
For example, given 1 8 4 9 0 2 , return 3. Thanks.
Solution
{⍬⍴(⍳1+⍴⍵)~⍵} 1 8 4 9 0 2
3
OTHER TIPS
The case where they are all used seems to have "one plus the largest" as the answer, but whether that is "from" the list is another question.
@Paul, are you using APL385 as your browser's font? That seems to have cleared up many things from this end.
Try
((⍳⍴n)∊n)⍳0
or
((iota rho n) element n) iota 0
This is more or less the standard idiom for choosing the next available file tie number.
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