Leetcode: Valid Tic-Tac-Toe State

Valid Tic-Tac-Toe State

A Tic-Tac-Toe board is given as a string array board. Return True if and only if it is possible to reach this board position during the course of a valid tic-tac-toe game.

The board is a 3 x 3 array, and consists of characters ” “, “X”, and “O”. The ” ” character represents an empty square.

Here are the rules of Tic-Tac-Toe:

  • Players take turns placing characters into empty squares (” “).
  • The first player always places “X” characters, while the second player always places “O” characters.
  • “X” and “O” characters are always placed into empty squares, never filled ones.
  • The game ends when there are 3 of the same (non-empty) character filling any row, column, or diagonal.
  • The game also ends if all squares are non-empty.
  • No more moves can be played if the game is over.
Example 1:
Input: board = ["O  ", "   ", "   "]
Output: false
Explanation: The first player always plays "X".
Example 2:
Input: board = ["XOX", " X ", "   "]
Output: false
Explanation: Players take turns making moves.
Example 3:
Input: board = ["XXX", "   ", "OOO"]
Output: false
Example 4:
Input: board = ["XOX", "O O", "XOX"]
Output: true


  • board is a length-3 array of strings, where each string board[i] has length 3.
  • Each board[i][j] is a character in the set {” “, “X”, “O”}.

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.

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