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how to solve this problem ?
By _Evoiz_, history, 6 years ago, In English

what is the best way to solve this problem ? game theory? we have N*M empty grid and we have two players each player in his turn take an empty cell and put "X" in it game end when a player can make line with three "X" (like tik-tak-too game) players play optimally so who is the winier in this game?

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6 years ago, # |
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Auto comment: topic has been updated by _Evoiz_ (previous revision, new revision, compare).

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6 years ago, # |
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Auto comment: topic has been updated by _Evoiz_ (previous revision, new revision, compare).

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6 years ago, # |
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What are the constraints on n, m? If they are very small, then we can do masking to solve this problem.

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6 years ago, # |
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Do diagonal lines also count?

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6 years ago, # |
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Edited: Sorry, I totally misunderstood problem.

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6 years ago, # |
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Since the player wins when 3 X's are together, the below solution assumes that either of m or n is greater than or equal to 3.

Player 1 wins only when both m and n are odd. Else player two will win.

The logic is simple. Suppose that either of m or n is not odd. Hence player 2 can always mimic turn of player 1 and upon getting appropriate chance it can make the winning move.

Where as if both m and n are odd, player 1 will place first X in the center square of grid and then player 1 will mimic each turn of player 2 thus on getting appropriate chance player 1 will make the winning move.

Thus player 1wins if both m and n are odd else player 2 wins

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    6 years ago, # ^ |
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    i think it's work , thank you.

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    6 years ago, # ^ |
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    Sorry, how can the second player win if we have 4x4 grid and the first player starts the game marking by "X" the field (2,2) (here it doesn't matter whether 0-based or 1-based coordinates are)?

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      6 years ago, # ^ |
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      i think if n or m less than or equal to two then their is no winner . or we can say that if player didn't find any empty cell he will be lose and game over . so we can see if n or m less than 3 this is special case, other this if n or m is even player 2 will wine

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      6 years ago, # ^ |
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      if n or m is even then i can split the grid to two grid (n*m/2) or (n/2*m) and the second player make move like the first player

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        6 years ago, # ^ |
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        We can't split it independently, the halfs will affect each other. In case of 4x4 grid and first step (2,2) the second player can't reply symmetrically, otherwise he looses.

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          6 years ago, # ^ |
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          so how we solve it in your opinion?

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    6 years ago, # ^ |
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    Assuming the grid is 3x3 (like the original tic-tac-toe), by your solution Player 1 is the winner, whereas when both playing optimally in original tic-tac-toe game (3x3 grid), the results are always end up in draws. It contradicts with your solution (I don't know the solution yet, though).

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      6 years ago, # ^ |
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      if the first player put "X" in the center of grid ,what ever player two put his "X" the first will can make a line with three "X" .

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    6 years ago, # ^ |
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    I didn't get, why if n is odd and m is even the second player wins. For example, if n = 3 and m = 4 then the first player can put X in cell (2, 2) (we suppose lines are numbered from 1 to 3 and columns from 1 to 4). Then the second player has to put in cell (2, 3), doesn't he? If he does, so the first player will win

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      6 years ago, # ^ |
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      that's true so we start again how to solve this problem ?

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6 years ago, # |
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Can you please provide link to the problem so that we can also learn

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    6 years ago, # ^ |
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    i am so sorry , their is no link because i write this problem and i didn't find a solution for it . i didn't see this problem in any other online judge before

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6 years ago, # |
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Quoting from this article. A 3-in-a-row game is a winning game for Player 1 if and only if N >= 3 and M >= 4 (number of row and column can be swapped). Otherwise, it's a draw game (3x3 or smaller grid).

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    6 years ago, # ^ |
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    it's not like tic-tak-too because the two players play with "X"

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      6 years ago, # ^ |
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      p1: put "X" in cell (2,2)(center);p2: put"X" in cell (1,1);p1: put"X" in cell(3,3) and p1 win

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        6 years ago, # ^ |
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        Ah, I see. I'm sorry I misunderstood your problem thinking that thr X from Player 1 and 2 are different.

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