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Post Challenge

Cumulative Counts

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Challenge

Given an array of numbers return the cumulative count of each item.

This is the number of times an item has occurred so far.

Examples

[1,1,2,2,2,1,1,1,3,3] -> [1,2,1,2,3,3,4,5,1,2]
[3,7,5,4,9,2,3,2,6,6] -> [1,1,1,1,1,1,2,2,1,2]

Brownie points for beating my 7 byte APL answer.

code-golf
posted about 4 years ago
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rak1507‭
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21 answers

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Lean 4, 111 bytes

def c(l:List Nat):List Nat:=((λx=>((l.reverse).drop x).count (l.reverse)[x]!)<$>(List.range l.length)).reverse

Try it online!

Given how verbose Lean syntax is, and how you can't really assign variables to keywords in a way that it saves bytes the vast majority of the time, if at all, I doubt there's a way to save any more bytes from here. I think 111 might actually be the limit.

And the only reason that I have to reverse the list is because while Lean does have a function to drop elements, it only does so from the left, which we really don't want here.

Hexdump since this contains unprintable characters:

00000000 64 65 66 20 64 28 6c 3a 4c 69 73 74 20 4e 61 74  |def d(l:List Nat|
00000010 29 3a 4c 69 73 74 20 4e 61 74 3a 3d 28 28 ce bb  |):List Nat:=((..|
00000020 78 3d 3e 28 28 6c 2e 72 65 76 65 72 73 65 29 2e  |x=>((l.reverse).|
00000030 64 72 6f 70 20 78 29 2e 63 6f 75 6e 74 20 28 6c  |drop x).count (l|
00000040 2e 72 65 76 65 72 73 65 29 5b 78 5d 21 29 3c 24  |.reverse)[x]!)<$|
00000050 3e 28 4c 69 73 74 2e 72 61 6e 67 65 20 6c 2e 6c  |>(List.range l.l|
00000060 65 6e 67 74 68 29 29 2e 72 65 76 65 72 73 65     |ength)).reverse|
posted 11 days ago
11d ago
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CrSb0001‭
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