【高级技巧】洪水填充：连通区域的标记算法

local function floodFill(grid, w, h, sx, sy, mark)
    local stack = { { sx, sy } }
    while #stack > 0 do
        local cell = table.remove(stack)
        local x, y = cell[1], cell[2]
        if x >= 1 and x <= w and y >= 1 and y <= h
            and grid[y][x] == 0 then
            grid[y][x] = mark
            stack[#stack + 1] = { x + 1, y }
            stack[#stack + 1] = { x - 1, y }
            stack[#stack + 1] = { x, y + 1 }
            stack[#stack + 1] = { x, y - 1 }
        end
    end
end

local grid = { { 0, 0, 1 }, { 0, 1, 1 }, { 0, 0, 0 } }
floodFill(grid, 3, 3, 1, 1, 9)
print(grid[1][1], grid[2][1], grid[3][3])