Sunday, June 01, 2008

Tic-Tac-Toe Tips

Since I am the greatest tic-tac-toe player in the world (actually tied with thousands for that title), I thought I'd write up a basic strategy for the game, whose secrets I cracked in high school study hall.


The Board & Basics






There are nine spaces or boxes in tic-tac-toe that can be played. They can be grouped into three categories:

The center square (5)
Corner squares (1,3,7,9)
Edge squares (2,4,6,8)

The goal as most know, is to get three of your symbol in a row. The only way this can be done, without counting on a silly oversight by your opponent, is to move in such a way that there becomes 2 ways for you to win - thus creating a situation where your opponent cannot block both of them.


Going First

If you have the first move, you should be playing to win. Although it is impossible for anyone to win if the opponent has optimum strategy (every game between two perfect players is a draw), many do not. You may think that with the first move you have nine spaces to choose from. You would be wrong. In reality, you only have three choices: center, corner, or edge. All the squares in a category are actually the same for the first move. Simply rotating the game board can prove this.

Corner Strategy

My preferred first move against an inexperienced opponent is to choose one of the corner squares. As mentioned above, it doesn't matter which one.

Non-Center Square Opponent Move

If your opponent does not then select the center square with their first square, you will win, your opponent can no longer stop you if you employ proper strategy. (The strategies listed are not necessary the only successful ones for the scenario, but are sufficiently unstoppable). When I say "guarantee your win" this means that you have set up a scenario where on your next turn you will have at least 2 ways to win, and your opponent can't stop both of them. Being forced to move somewhere means that you (or the opponent) must select a certain space to prevent a win.

For example if your first move was square 1:

and you opponent selects square 2, then play square 7. When your opponent is forced to play square 4, then play square 3, 5, or 9 to guarantee your win.

… selects square 3, then play square 7. When your opponent is forced to play square 4, then play square 9 to guarantee your win.

… selects square 4, then play square 3. When your opponent is forced to play square 2, then play square 5 or 9 to guarantee your win.

… selects square 6, the play square 3. When your opponent is forced to play square 2, then play square 5 or 7 to guarantee your win.

… selects square 7, then play square 3. When your opponent is forced to play square 2, then play square 9 to guarantee your win.

… selects square 8, then play square 7. When your opponent is forced to play square 4, then play square 3 or 5 to guarantee your win.

… selects square 9, then play square 3. When your opponent is forced to play square 2, then play square 7 to guarantee your win.

The scenarios for your corner moves starting in 3, 7, or 9 are, as you would expect, remarkably similar and are left as an exercise to the reader.

Center Square Opponent Move

If your opponent makes his first move in the center square (remember this after you have moved in a corner square), you will have a much tougher time winning. In fact your only chance for a guaranteed win, barring a catastrophic blunder from your opponent, is to make your next move in the opposite corner and hope your opponent then selects another corner for his second move.

That is, if your select square 1, your opponent selects square 5, then you should select square 9. If you opponent then selects either 3 or 7 you can select the remaining corner square and guarantee your win.


Center Square Strategy

As an alterative to the corner first strategy, you may want to consider selecting the center square with your first move. This offers fewer chances to win then the corner first strategy, but is a nice mix-up to someone who is becoming wise to the corner first strategy.

Edge Square Opponent Move

If in response to your center square selection, your opponent selects an edge square, you can be certain of victory. Assuming you use correct strategy of course. Once again, the strategies listed are not necessary the only successful ones for the scenario, but are sufficiently unstoppable.

For example if your first move was square 5:

and you opponent selects square 2, then play square 3. When your opponent is forced to play square 7, then play square 6 or 9 to guarantee your win.

… selects square 4, then play square 1. When your opponent is forced to play square 9, then play square 3 or 7 to guarantee your win.

… selects square 6, then play square 9. When your opponent is forced to play square 1, then play square 7 or 8 to guarantee your win.

… selects square 8, then play square 7. When your opponent is forced to play square 3, hen play 1 or 4 to guarantee your win.

Corner Square Opponent Move

If in response to your center square selection, your opponent selects a corner square, you will have a much harder time wining. In fact your only chance for a guaranteed win, barring a catastrophic blunder from your opponent, is to make your next move in the opposite corner of your opponents move, and then hope your opponent selects an edge square with their second selection.
For example, if you select square 5 with the first move, and your opponent selects square 1, and in response you select square 9, then if

you opponent selects square 2, then you are forced to play square 3, and this gives you a guaranteed win.

… plays square 4, then you are forced to play square 7, and this gives you a guaranteed win.

… plays square 6, then you play square 8, giving yourself a guaranteed win.

… plays square 8, then you play square 6, giving yourself a guaranteed win.

The scenarios for the opponent's first move in a corner other than square 1 are, as you would expect, remarkably similar and are left as an exercise to the reader.


Edge Square Strategy

Your other option when making the first selection is to select an edge square. As this is the weakest first move, it is not recommended for beginning players.


Going Second

Of course, you do not always get to go first. When you are playing second, your goal should be to force a cat game (that is, a draw) because you cannot win unless your opponent makes a very grievous mistake.

The golden rule of going second is this: If your opponent doesn't take the center square, you must take it. And if your opponent does take the center square, you must take a corner square. This solves approximately 90% of the problems of going second. All you have to do from there is to avoid the secondary pitfalls. Most of these can be determined from the going first section, just put yourself and the place of the opponent.

Good night and good luck.

Not that luck is a factor in tic-tac-toe.

3 Comments:

Blogger Ma Hoyt said...

It's about time you posted!

I thought maybe the cockroach had gotten you.

4:07 PM, June 14, 2008  
Blogger Melchizedek said...

Nope. And I figured the cockroach out, it was a different type of one that normally stays outside.

6:17 PM, June 14, 2008  
Blogger SarahH said...

Wow... That's a pretty neat little summary. I used to play on the back of church bulletins with my friends, and I sort of knew most of this at the time, but without thinking about why it was helping me win.

9:49 AM, October 15, 2008  

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