Tic Tac Toe Blindfolded Strategy
[ - fun - Certus]
https://fivethirtyeight.com/features/can-you-win-tic-tac-toe-blindfolded/
I’m using the rules set by this puzzle on FiveThirtyEight.
You start, so you can always put an X in the corner (1, 3, 7, or 9). Let’s say 1 for simplicity.
X 2 3
4 5 6
7 8 9 <- place in 1
Your opponent makes a move. You place your next X in 3, if you can. If you can’t, put An X in 7, which you are guaranteed to be able to do because your opponent has only made one move into 3.
X 2 O
4 5 6
X 8 9 <- 3 is filled, place in 7
As far as you are concerned, your opponent has 2 options, they can put an O in 4, or not. So, your next move should be to put an X in 4. If you can, you win directly.
X 2 O
X 5 6
X 8 9 <- place in 2, win
If not you can place an X in 9, guaranteeing a win in the next move by placing in either 5 or 8, whichever is open.
X 2 O
O 5 6
X 8 X <- 2 is filled, place in 9, win by 5 or 8
If your opponent does not place in 3, your next move should be to try to put an X in 2, a direct win.
X X X
4 5 6
7 8 9 <- place in 3, win
If your opponent has an O in 2, you should try to put an X in 5.
X O X
4 5 6
7 8 9 <- 2 is filled, try 5
If you can’t do that either, you should put an X in 8 because your opponent has 2 O’s in a row.
X O X
4 O 6
7 X 9 <- 5 is filled, place in 8
From this position, you should place in either 4 or 6, depending on which is open, to ensure that your opponent cannot win.
X O X
X O 6
7 X 9 <- place in 4
X O X
O O X
7 X 9 <- 4 is filled, place in 6
After that, if you placed in 4, you should try to win in 7, and if you placed in 6, you should try to win in 9. Otherwise the game will end in a tie.
X O X
X O 6
X X 9 <- place in 4, then 7, win
X O X
O O X
7 X X <- place in 6, then 9, win
X O X
X O 6
O X 9 <- place in 4, 7 is filled, tie
X O X
O O X
7 X O <- place in 6, 9 is filled, tie
If you were able to place in 5, your next move should be in 7, earning you a win.
X O X
4 X 6
X 8 9 <- place in 5, then 7, win
If 7 is filled, try 9, also earning a win.
X O X
4 X 6
O 8 X <- 7 is filled, place in 9, win
If they are both already filled, you should place in 8 to prevent your opponent from winning. From this position, neither you nor your opponent can win.
X O X
4 X 6
O X O <- 9 is filled, place in 8, tie
With this strategy, you will never lose, and you may even win.