Sudoku Solver 4x4

board = {}
shell.run("delete console")
local h = fs.open("console","a")

function createEmptyBoard()
    for i = 1,4 do
        board[i] = {}
        for j = 1,4 do
            board[i][j] = {}
            board[i][j].num = 0
            board[i][j].exceptions = {}
            board[i][j].options = {}
        end
    end
end

function printBoard()
    for i=1,4 do
        for j=1,4 do
            term.setCursorPos(i,j)
            term.write(board[i][j].num)
        end
    end
end

--==Sudoku Functions==--
function findEmpty()
    for y = 1,4 do
        for x = 1,4 do
            if board[x][y].num == 0 then
                return true,x,y
            end
        end
    end
end

local function findQuadrant(x,y)
    quadrant = {}
    quadrant.num = 0
    quadrant.x = 0
    quadrant.y = 0
    if x <= 2 then
        if y<=2 then
            quadrant.num = 1
            quadrant.x = 1
            quadrant.y = 1
        elseif y<=4 then
            quadrant.num = 3
            quadrant.x = 1
            quadrant.y = 3
        end
    elseif x<=4 then
        if y<=2 then
            quadrant.num = 2
            quadrant.x = 3
            quadrant.y = 1
        elseif y<=4 then
            quadrant.num = 4
            quadrant.x = 3
            quadrant.y = 3
        end
    end
    return quadrant
end


local function organizeOptions(x,y)
    for i=1,9 do
        board[x][y].options[i] = i
    end
    for i = 1,9 do
        for _,k in pairs(board[x][y].exceptions) do
            if i == k then
                board[x][y].options[i] = 0
            end
        end
    end
end

function findOptions(x,y)
    for i = 1,4 do
        if board[i][y].num ~= 0 then
            table.insert(board[x][y].exceptions,board[i][y].num)
        end
        if board[x][i].num ~= 0 then
            table.insert(board[x][y].exceptions,board[x][i].num)
        end
    end
    quadrant = findQuadrant(x,y)
    for i = quadrant.x,quadrant.x+1 do
        for j = quadrant.y,quadrant.y+1 do
            if board[i][j].num ~= 0 then
                table.insert(board[x][y].exceptions,board[i][j].num)
            end
        end
    end
    organizeOptions(x,y)
end


function recursive()
    unsolved,x,y = findEmpty()
    if unsolved then
        findOptions(x,y)
        for _,v in pairs(board[x][y].options) do
            if v~= 0 then
                board[x][y].num = v
                recursive()
            end
        end
        board[x][y].num = 0
    else
        printBoard()
        print("FINISHED :D")
        error()
    end
end

--==Debug Functions==--

function fillRand()
    for i=1,4 do
        for j=1,4 do
            board[i][j].num = math.random(1,9)
        end
    end
end

function tab(t)
    for i,v in pairs(t) do
        if type(v) == "table" then
            tab(v)
        else
            print("i: ",i," v: ",v)
        end
    end
end

function log(s)
    if type(s) == "string" then
        h.writeLine(s)
    else
        for i,v in pairs(s) do
            h.write("i: ")
            h.write(i)
            h.write(" v: ")
            h.writeLine(v)
        end
    end
    h.flush()
end


createEmptyBoard()
term.clear()
board[1][1].num = 8
board[2][1].num = 3
board[3][2].num = 6
board[4][2].num = 2
board[2][3].num = 1
board[4][3].num = 5
board[4][4].num = 4

--fillRand()
recursive()