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.
class Solution: # Time: O(1) - the board is always 3 x 3 # Space: O(1) def valid_tic_tac_toe(self, board: list[str]) -> bool: x_count = sum(row.count("X") for row in board) o_count = sum(row.count("O") for row in board) if o_count not in (x_count - 1, x_count): return False x_wins = self._wins(board, "X") o_wins = self._wins(board, "O") if x_wins and o_wins: return False if x_wins: return x_count == o_count + 1 if o_wins: return x_count == o_count return True def _wins(self, board: list[str], player: str) -> bool: lines = [board[i] for i in range(3)] lines += ["".join(row[j] for row in board) for j in range(3)] lines.append("".join(board[i][i] for i in range(3))) lines.append("".join(board[i][2 - i] for i in range(3))) return any(line == player * 3 for line in lines)
