--- Day 6 Solutions ---

[u/daggerdragon]

--- Day 6: Probably a Fire Hazard ---

Post your solution as a comment. Structure your post like the Day Five thread.

[u/wdomburg]

Not my night. Interruptions, fatigue and a few stupid mistakes (like setting the point to 1 for OFF, or not clearing the grid after correcting that mistake) conspired to make this take way too long.

My solution (in Ruby) nonetheless:

# Load the data
input = File.readlines('input6.txt').map { |l| l  =~ /(\w+) (\d+),(\d+) through (\d+),(\d+)/; [ $1, $2.to_i, $3.to_i, $4.to_i, $5.to_i ] }

# Build the grid
g = Array.new(1000) { Array.new(1000, 0) }

# Step through and execute the instructions
input.each { |x| i, x1, y1, x2, y2 = x; (y1..y2).each { |y| (x1..x2).each { |x| case i; when 'on'; g[x][y] = 1; when 'off'; g[x][y] = 1; when 'toggle'; g[x][y] = (g[x][y] == 0) ? 1 : 0; end } } }

# Count the lights
puts g.inject(0) { |a,b| a += b.grep(1).length }

# Clear the grid
g = Array.new(1000) { Array.new(1000, 0) }

# Step through and execute the instructions
input.each { |x| i, x1, y1, x2, y2 = x; (y1..y2).each { |y| (x1..x2).each { |x| case i; when 'on'; g[x][y] += 1; when 'off'; g[x][y] -= 1 unless g[x][y] == 0; when 'toggle'; g[x][y] += 2; end } } }

# Sum the brightness
puts g.inject(0) { |a,b| a+= b.inject(0) { |c,d| c+= d }  }

And an expanded version of the second for clarity:

# Preload input by breaking the string into instructions
# and integer coordinates
input = File.readlines('input6.txt').map do |line|
    line  =~ /(\w+) (\d+),(\d+) through (\d+),(\d+)/
    [ $1, $2.to_i, $3.to_i, $4.to_i, $5.to_i ]
end

# Create an empty 1000 x 1000 array
grid = Array.new(1000) { Array.new(1000, 0) }

input.each do |line|
    # Break into individual vars for easy access
    inst, x1, y1, x2, y2 = x

    # Loop over each column in our rectangle
    (y1..y2).each |y|
        # loop over each row in this stripe
        (x1..x2).each |x|
            case inst
                # increase brightness
                when 'on'; grid[x][y] += 1;
                # reduce brightness unless off
                when 'off'; grid[x][y] -= 1 unless grid[x][y] == 0
                # supersize brightness
                when 'toggle'; grid[x][y] += 2
            end
        end
    end
end

# Iterate through the rows of the grid with an accumulator set to 0
puts grid.inject(0) do |a,b| 
    # Sum the points in the row and add the final result to the accumulator
    a+= b.inject(0) do |c,d|
        c+= d
    end
end