Propagating Rotten Oranges

oranges.rb

NOTHING = 0
FRESH_ORANGE = 1
ROTTEN_ORANGE = 2

# @param {Integer[][]} grid
# @return {Integer}
def oranges_rotting(grid)
    # Search the grid for rotten oranges
    next_step = scan_grid(grid, ROTTEN_ORANGE)
    this_step = []
    
    count = 0
    while !next_step.empty? do
        this_step, next_step = next_step, this_step
        
        while !this_step.empty? do
            y, x = this_step.pop
            rot_surrounding(grid, y, x, next_step)
        end
        count += 1 if !next_step.empty?
    end
    scan_grid(grid, FRESH_ORANGE).empty? ? count : -1
end

def rot_surrounding(grid, y, x, next_step)
    height = grid.length
    width = grid[0].length
    mutations.each do |(dy, dx)|
        adj_x = x + dx
        adj_y = y + dy
        if (0...height).include?(adj_y) && (0...width).include?(adj_x) && grid[adj_y][adj_x] == FRESH_ORANGE
            grid[adj_y][adj_x] = ROTTEN_ORANGE
            next_step.push([adj_y, adj_x])
        end
    end
end

def mutations
    [
        [-1, 0],
        [0, -1],
        [0, 1],
        [1, 0],
    ]
end

def scan_grid(grid, type)
    found = []
    grid.each_with_index do |row, y|
        row.each_with_index do |cell, x|
            found.push([y, x]) if cell == type
        end
    end
    found
end