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Given a Tic-Tac-Toe board 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 that 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 three 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.length == 3
  • board[i].length == 3
  • board[i][j] is either 'X', 'O', or ' '.

class Solution { public boolean validTicTacToe(String[] board) { } }