CodinGame: There is no Spoon - Episode 1

there-is-no-spoon-1.lua

-- Don't let the machines win. You are humanity's last hope...

local function debug(fmt,...)
    io.stderr:write(string.format(fmt,...))
end

local function outputCoords(x1,y1,x2,y2,x3,y3)
    io.write(string.format("%d %d %d %d %d %d\n",x1,y1,x2,y2,x3,y3))
end

local function outputInvalid(fmt,...)
    if fmt then debug(fmt,...) end
    outputCoords(-1,-1,-1,-1,-1,-1)
end

-- assume header data is always correct because we prioritise speed :/
local width = tonumber(io.read()) -- the number of cells on the X axis
local height = tonumber(io.read()) -- the number of cells on the Y axis

local data = {}

local function getNode(w,h)
    repeat
        if data[w] then
            if data[w][h] then
                -- debug("getNode(%d,%d) = %q\n",w,h,data[w][h])
                return data[w][h]
            end
        end
        
        if w >= width then return false end
        if h >= height then return false end
        
        coroutine.yield()
    until false
end

local done = false
local function scan()
    for h=0,height-1 do
        for w=0,width-1 do
            local currentNode = getNode(w,h)
            
            local x2,y2 = -1,-1
            local x3,y3 = -1,-1
            
            if currentNode then
                -- sweet, we are a node
                
                for offset=1,(width - w) do
                    if getNode(w + offset,h) then
                        x2,y2 = w + offset,h
                        break
                    end
                end
                
                for offset=1,(height - h) do
                    if getNode(w,h + offset) then
                        x3,y3 = w,h + offset
                        break
                    end
                end
                
                outputCoords(w,h,x2,y2,x3,y3)
            end
        end
    end
    
    done = true
end
scan = coroutine.wrap(scan)

local function safeResume()
    if not done then return scan() end
end

for h=0,height-1 do
    line = io.read() -- width characters, each either 0 or .
    for w=0,width-1 do
        local datum = line:sub(w + 1,w + 1)
        
        if not datum or (datum == "") then
            -- uh oh?
            debug("couldn't read column data for row %d past column %d",h,w)
            break
        end
        
        if (datum == ".") or (datum == "0") then
            data[w] = data[w] or {}
            data[w][h] = datum ~= "."
        
            safeResume()
        else
            debug("column data is neither '.' nor '0'??? (%q)",datum)
        end
    end
end
        
safeResume()

xpcall(main,function(e)
    outputInvalid("fatal: %s",debug.traceback(e))
end)