We can represent a Tic-Tac-Toe board as a 3 × 3 grid in which each position can hold one of the following three strings: "X", "O", or " ". Write a function named check_winner that accepts a 3 × 3 list...

We can represent a Tic-Tac-Toe board as a 3 × 3 grid in which each position can hold one of the following three strings: "X", "O", or " ". Write a function named check_winner that accepts a 3 × 3 list as a parameter. If "X" appears in a winning Tic-Tac-Toe pattern, the function should return the string "X". If "O" appears in a winning Tic-Tac-Toe pattern, the function should return the string "O". If no winning pattern exists, the function should return the string " ".