input: Write a python function to check if a player has won in a tic-tac-toe game.
  assert win_check('X') == True
  assert win_check('O') == False
  assert win_check('X') == False
output: def win_check(board, player):
      # Check rows
      for row in board:
          if all(s == player for s in row):
              return True
  
      # Check columns
      for col in range(len(board)):
          if all(board[row][col] == player for row in range(len(board))):
              return True
  
      # Check diagonals
      if all(board[i][i] == player for i in range(len(board))):
          return True
      if all(board[i][len(board)-1-i] == player for i in range(len(board))):
          return True
  
      return False