1275 find winner on a tic tac toe game

1. Find Winner on a Tic Tac Toe Game

Easy

Tic-tac-toe is played by two players A and B on a 3 x 3 grid. The rules of Tic-Tac-Toe are:

• Players take turns placing characters into empty squares ' '.
• The first player A always places 'X' characters, while the second player B always places 'O' characters.
• 'X' and 'O' characters are always placed into empty squares, never on 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.

Given a 2D integer array moves where moves[i] = [rowi, coli] indicates that the ith move will be played on grid[rowi][coli]. return the winner of the game if it exists (A or B). In case the game ends in a draw return "Draw". If there are still movements to play return "Pending".

You can assume that moves is valid (i.e., it follows the rules of Tic-Tac-Toe), the grid is initially empty, and A will play first.

Example 1:

Input: moves = [[0,0],[2,0],[1,1],[2,1],[2,2]]
Output: "A"
Explanation: A wins, they always play first.

Example 2:

Input: moves = [[0,0],[1,1],[0,1],[0,2],[1,0],[2,0]]
Output: "B"
Explanation: B wins.

Example 3:

Input: moves = [[0,0],[1,1],[2,0],[1,0],[1,2],[2,1],[0,1],[0,2],[2,2]]
Output: "Draw"
Explanation: The game ends in a draw since there are no moves to make.

Constraints:

• 1 <= moves.length <= 9
• moves[i].length == 2
• 0 <= rowi, coli <= 2
• There are no repeated elements on moves.
• moves follow the rules of tic tac toe.

Solution

class Solution:
    def tictactoe(self, moves: List[List[int]]) -> str:
        rows = [[0] * 3 for _ in range(2)]
        cols = [[0] * 3 for _ in range(2)]
        diag1 = [0] * 2
        diag2 = [0] * 2
        p = 0

        for r, c in moves:
            rows[p][r] += 1
            cols[p][c] += 1
            if r == c:
                diag1[p] += 1
            if r + c == 2:
                diag2[p] += 1

            if 3 in (rows[p][r], cols[p][c], diag1[p], diag2[p]):
                if p == 0:
                    return "A"
                else:
                    return "B"

            p = 1 - p

        if len(moves) < 9:
            return "Pending"
        else:
            return "Draw"