Goplat's 15Puzzle for TI-nspire Lua

Anyway good to see that we won't have to take to such measures of making Lua scripts run in the future and can even edit the file directly (which means even better than Oclua on calc!). But to get back on topic
I want to try and understand completely what Goplat's 15 puzzle means. I've already learnt quite a bit, let's see what else there is. I have commented on this within the code Cheesy

Code: Select All | Copy To Clipboard

function on.charIn(ch) --called when a character key is pressed
 if ch == "r" then --when r is pressed
  board = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 } --this is how you create arrays!
  -- Randomize
  local swaps = 0  -- a local variable (wonder why)
  for i = 1, 16 do   -- ah this is the For...To syntax in TI-84 and Casio basic and other stuff
   local j = math.random(i, 16)  -- local variable, random number from i to 16
   if i ~= j then  -- i not equal to j
    board[i], board[j] = board[j], board[i]     --swap number in position i and j?
    swaps = swaps + 1  --swaps number of turns
   end
   if board[i] == 16 then  --reach the end
    empty = i  
   end
  end

  -- If the number of swaps plus the number of empty-space movements is odd,
  -- then the puzzle is impossible, so do an impossible move to make it possible
  -- (exchange the space with a tile two squares away)
  if (swaps + (empty - 1) + math.floor((empty - 1) / 4)) % 2 == 1 then   -- not 100% how this works, I know this is a way to fix an impossible puzzle :P
   local i = (empty + 7) % 16 + 1
   board[empty] = board[i]
   empty = i
   board[empty] = 16
  end

  moves = 0
  platform.window:invalidate()  --force redraw of the screen calls on.paint(gc)
 end
end

on.charIn("r")

function on.paint(gc)
 local won = true
 for i, n in ipairs(board) do
  if n ~= 16 then
   local x = (platform.window:width() - 128) / 2 + 32*((i - 1) % 4)
   local y = (platform.window:height() - 128) / 2 + 32*math.floor((i - 1) / 4)
   gc:drawRect(x, y, 30, 30)
   gc:drawString(n, x + (30 - gc:getStringWidth(n)) / 2, y + 15, "middle")
  end
  won = (won and n == i)
 end

 local str = moves .. " moves"
 gc:drawString(str, (platform.window:width() - gc:getStringWidth(str)) / 2, 0, "top")
 if won then
  str = "You win! Press R to reset"
  gc:drawString(str, (platform.window:width() - gc:getStringWidth(str)) / 2, platform.window:height(), "bottom")
 end
end

function on.arrowKey(key)
 local dir
 if key == "left" and empty % 4 ~= 0 then
  dir = 1
 elseif key == "right" and empty % 4 ~= 1 then
  dir = -1
 elseif key == "up" and empty <= 12 then
  dir = 4
 elseif key == "down" and empty > 4 then
  dir = -4
 else
  return
 end
 board[empty] = board[empty + dir]
 empty = empty + dir
 board[empty] = 16
 moves = moves + 1
 platform.window:invalidate()
end