hey @Adám, do you have any ideas on how to implement flood fill on a 2d boolean matrix in APL

@KamilaSzewczyk I did one for previous Advent of Code questions a matrix that 2 means boundary and 1 means color, {⍵⌈{∨/,1=g×⍵}⌺3 3⊢⍵}⍣≡ should work

given g←3 3⍴0 1 0 1 0 1 0 1 0 for four direction and g←1 for eight direction

⋄ {⍵⌈{∨/,1=(3 3⍴(9⍴2)⊤170)×⍵}⌺3 3⊢⍵}⍣≡⊢3 3⍴1 2 0 0 2 0 0 0 2

@LdBeth
1 2 0
1 2 0
1 1 2

@KamilaSzewczyk Yeah, ⌺ is the way to go.

Why is in a dfn '1,2,3' printed as 3 2 1 and typed in the workspace 1 2 3?

@Richard What‽ ⎕←{1,2,3}⍬

@Adám 1 2 3

then something strange is happening in my dfn

There's this:

      (⍞←1)(⍞←2)(⍞←3)
321
1 2 3

its one of the phase 1 problems which prints my solution the other way around

But you should return a result, not print it "manually".

can I share it? And delete is afterwards? Its not very complicated.

No, history is public. However, you can email it to me.

Fine. just look at the structure. Don't give any solution of course :)