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Marco Servetto
Marco Servetto

Posted on

Advent of code Day 9

I'm very satisfied for my solution today.
This problem fits very well with AdamsTowel matrixes.
You can see a video description of my solution at
(https://www.youtube.com/watch?v=tSTDJlICst8)
Some highlights of the solution:
(1)

(new=that.with(row=\row-1\) catch error Any _ void \add(new))
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This is making a new coordinate and adding it to the list under construction. If the coordinate would be outside of the matrix, an error is raised and ignored.
(2)

sizes=I.List()( for i in Range(seeds.size()) 
    \add(Match.Count()(for v in matrix \add(v==i+100I)))
    )
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Here we taint the seeds using a number much bigger than any height.
The number can be tracked back as the corresponding seed index.

(3)

GrowBasin={class method Void(mut Matrix matrix)=(
  for c in matrix.coords() var h in matrix {
    if h>=9I return void
    return for ci in Near(c) if matrix.val(ci)>99I return h:=matrix.val(ci)
    }
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To grow a basin one step, we search for all the coordinates c of height h; if there is a ci near c that is tainted with a basin number, we taint the current height too.

Here is the full code.

reuse [L42.is/AdamsTowel]

Fs = Load:{reuse[L42.is/FileSystem]}

Matrix = Collection.matrix(I.List,row=100I, col=100I)

Coords = Collection.list(Matrix.Coord)

Split={class method S.List (S that)=\()(//should be in adamsTowel
  for c in that.replace(S"" with=S",").split(S",")\add(c)
  )}
Near={class method Coords (Matrix.Coord that)=Coords()((
  (new=that.with(row=\row-1\) catch error Any _ void \add(new))
  (new=that.with(row=\row+1\) catch error Any _ void \add(new))
  (new=that.with(col=\col-1\) catch error Any _ void \add(new))
  (new=that.with(col=\col+1\) catch error Any _ void \add(new))
  ))}
GrowBasin={class method Void(mut Matrix matrix)=(
  for c in matrix.coords() var h in matrix {
    if h>=9I return void
    return for ci in Near(c) if matrix.val(ci)>99I return h:=matrix.val(ci)
    }
  )}
NeedsMore={class method Bool(read Matrix matrix) = 
  Match.Some()(for e in matrix \add(e<9I))  
  }
PopMax ={class method I (mut I.List that)=(
  var i = 0I
  var e = 0I
  for ei in that, ii in Range(that.size()) if ei>e (
    e:=ei, i:=ii
    )
  that.remove(i)
  e
  )}

MainPart2 = (
  input = Fs.Real.#$of().read(\"input")
  matrix = Matrix(\()(
    for s in input.split(S.nl()) for si in Split(s) \add(I(string=si))
    ))
  seeds = Coords()(for c in matrix.coords() h in matrix (
    min = Match.All()(for ci in Near(c) \add(matrix.val(ci)>h))
    if min \add(c)
    ))
  for c in seeds, i in Range(seeds.size()) (matrix.set(c val=i+100I))
  while NeedsMore(matrix=matrix) ( GrowBasin(matrix=matrix) )
  sizes=I.List()( for i in Range(seeds.size()) 
    \add(Match.Count()(for v in matrix \add(v==i+100I)))
    )
  v1=PopMax(sizes)
  v2=PopMax(sizes)
  v3=PopMax(sizes)
  Debug(v1*v2*v3)//882942
  )

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