def drop$\_$disc$\_$one$\_$square$($board$,$ x$,$ y$)$: def can$\_$disc$\_$fall$($board$,$ x$,$ y$)$:

$""!"$

Given board and x$,$y location.

Assume $\}$x$,$y$\backslash$mathrm$\{$ is in bounds and contains a disc.

Is moving the disc down one square ok$?$

Return True if the disc can fall, or False otherwise.

Disc can fall if the square exactly one space downward is in bounds and empty.Out$-$of$-$bounds $($O$0$B$)$ testsboard $=[[\text{'}$y$\text{'}]]$Falseboard $=[[$None$,\text{'}$r$\text{'},$ None$],[$None$,$ None, $\text{'}$y$\text{'}]]$TrueFalseboard $=[[$None$,$ None$],[\text{'}$r$\text{'},\text{'}$y$\text{'}]]$False

$"""$

# TODO: What y$-$location should you check is in bounds and doesn't already have a disc?

return False def update$\_$whole$\_$board$($board$)$:

$"""$

Given board, do one round of falling discs over the whole board.

If there is no disc at a location, no need to change the board.

If there is a disc, check if it can fall, then drop the disc,

one square at a time. Call your helper functions from above!

Return the board in all cases.

$($tests provided, code TBD$)$update$\_$whole$\_$board$($board$)$

$[[\text{'}$y$\text{'},\text{'}$r$\text{'},\text{'}$y$\text{'}],[$None$,$ None, $\text{'}$r$\text{'}],[$None$,\text{'}$y$\text{'},$ None$]][[\text{'}$y$\text{'},\text{'}$r$\text{'},\text{'}$y$\text{'}],[$None$,$ None, $\text{'}$r$\text{'}],[$None$,$ None, $\text{'}$y$\text{'}]]$

$""!$for y in reversed$($range$($len$($board$[0])))$:

for x in range$($len$($board$))$:pass

return board

def check$\_$horizontal$\_$win$($board$,$ player$)$:

$""!"$

Takes in the board and a player's token $(\text{'}$y$\text{'}$ for player $1$

or $\text{'}$r$\text{'}$ for player $2).$

Returns True if the player has $4$ tokens in a row horizontally

anywhere on the board and False if otherwise.

$""!"$

for y in range$($len$($board$[0]))$:

for x in range$($len$($board$)-3)$:pass

return False def check$\_$vertical$\_$win$($board$,$ player$)$:

$""!$

Takes in the board and a player's token $(\text{'}$y$\text{'}$ for player $1$

or $\text{'}$r$\text{'}$ for player $2).$

Returns True if the player has $4$ tokens in a row vertically

anywhere on the board and False if otherwise.

$""!$

for y in range$($len$($board$[0])-3)$:

for x in range$($len$($board$))$:pass

return False

def check$\_$diagonal$\_$wins$($board$,$ player$)$:

$"*"!$

PROVIDED $($DO NOT EDIT$)$

Takes in a board and a player's token.

Check if that player wins by getting $4-$in$-$a$-$row in two diagonal

directions, top$-$left$-$to$-$down$-$right and bottom$-$left$-$to$-$top$-$right.

$""!$for y in range$($len$($board$[0])-3)$:

for x in range$($len$($board$)-3)$:

if $($

board$[$x$][$y$]==$ player

and board$[$x$+1][$y$+1]==$ player

and board$[$x$+2][$y$+2]==$ player

and board$[$x$+3][$y$+3]==$ player

:

return Truefor y in range$($len$($board$[0])-3)$:

for x in range$(3,$ len$($board$))$:

if $($

board$[$x$][$y$]==$ player

and board$[$x$-1][$y$+1]==$ player

and board$[$x$-2][$y$+2]==$ player

and board$[$x$-3][$y$+3]==$ player

:

return Truedef check$\_$win$($board$,$ player$)$:

$"!"$

Takes in a board and a player's token.

Check if that player wins by calling each helper boolean function.

Return True if the player wins in any of the $3$ ways, False if not.

$"\backslash$prime$"!$Hint: this is where decomposition helps with readability!

is$\_$player$\_$diagonal$\_$winner $=$ check$\_$diagonal$\_$wins$($board$,$ player$)$

return is$\_$player$\_$diagonal$\_$winner

def is$\_$full$($board$)$:

$"\backslash$prime$\backslash$prime$\backslash$prime

PROVIDED $($DO NOT EDIT$)$

Take in a board and return True if all the slots are filled.

Ignores the top row since that is invisible and not treated as the board.

$"\backslash$prime$")$

for y in range$(1,$ len$($board$[0]))$:

for x in range$($len$($board$))$:

if board$[$x$][$y$]$ is None:

return False

return True

$"!"$

Given board and x$,$y location containing a disc.

Move the disc one square downwards and return the resulting board.

Assume that this is a legal move: all coordinates are in

bounds, the location contains a disc, and the square below is empty.

$($i$.$e$.$ a different function checks that this is a

legal move before drop$\_$disc$\_$one$\_$square$()$ is called$)$

Note: the board is a list of $($equally$-$lengthed$)$ lists. Each inner list

represents one whole column in the board. For example, board$[0]$

is the entire first column in the Connect$4$ board, from top to bottom.

$($tests provided, code TBD$)$drop$\_$disc$\_$one$\_$square$($board$,1,0)$

$[[$None$,\text{'}$r$\text{'},\text{'}$y$\text{'}],[$None$,\text{'}$y$\text{'},$ None$]]$board $=[[\text{'}$r$\text{'},\text{'}$y$\text{'},$ None$],[$None$,\text{'}$y$\text{'},$ None$]][[\text{'}$r$\text{'},\text{'}$y$\text{'},$ None$],[$None$,$ None, $\text{'}$y$\text{'}]]$

$""!$

disc $=$ board$[$x$][$y$]$ # is either $\text{'}$y$\text{'}$ for Player Yellow or $\text{'}$r$\text{'}$ for Player Redcurrent location and write it again at the square below?

return board