AOC 2024 Day 10, easy count paths/count destinations

aoc_2024_day10.rb

# frozen_string_literal: true

def neighbours(input, i, j)
  # @formatter:off
  @deltas ||= [
            [-1, 0],
    [0, -1],        [0, 1],
            [1, 0],
  ]
  # @formatter:on

  r = input.length
  c = input[0].length

  @deltas.map { |di, dj|
    [i + di, j + dj]
  }.select { |ix, jx|
    0 <= ix && ix < r && # row within bounds
      0 <= jx && jx < c # column within bounds
  }
end

input = DATA.read.strip.split("\n").map { |l| l.split("").map { |c| c == "." ? nil : c.to_i } }

def find_zeroes(input)
  trail_heads = []

  input.each_with_index.map do |r, i|
    r.each_with_index do |c, j|
      if c == 0
        trail_heads << [i, j]
      end
    end
  end

  trail_heads
end

def hike(input, i, j)
  cell = input[i][j]

  if cell == 9
    return [[i, j]]
  end

  walkable = neighbours(input, i, j).select { |ni, nj|
    input[ni][nj] == cell + 1
  }

  walkable.flat_map { |ni, nj|
    hike(input, ni, nj)
  }
end

zeroes = find_zeroes(input)
pp zeroes.sum { |zi, zj| hike(input, zi, zj).length } # should be 81

__END__
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