State of Tic-Tac-Toe2026-04-26

My Solution: Exercism State of Tic-Tac-Toe solution

Instructions

Determine the current state of a tic-tac-toe board.

Rules:

• Return whether the game is win, draw, or ongoing.
• Raise ValueError for impossible boards or invalid turn order.
• A board is won when a player has three marks in a row, column, or diagonal.

Solution

def gamestate(board):

    win_boxes = [
        [(0, 0), (0, 1), (0, 2)], [(1, 0), (1, 1), (1, 2)], [(2, 0), (2, 1), (2, 2)],
        [(0, 0), (1, 0), (2, 0)], [(0, 1), (1, 1), (2, 1)], [(0, 2), (1, 2), (2, 2)],
        [(0, 0), (1, 1), (2, 2)], [(0, 2), (1, 1), (2, 0)]           
    ]

    total_x = 0
    total_o = 0
    for line in board:
        line = line.replace(" ", "")
        for ch in line:
            if ch == 'X':
                total_x += 1
            else:
                total_o += 1

    if total_x - total_o >= 2:
        raise ValueError("Wrong turn order: X went twice")
    if total_o > total_x:
        raise ValueError("Wrong turn order: O started")

        
    occupied_boxes = total_o + total_x

    x_wins = False
    o_wins = False
    for route in win_boxes:
        cord1, cord2, cord3 = route 

        item_cord1 = board[cord1[0]][cord1[1]]
        item_cord2 = board[cord2[0]][cord2[1]]
        item_cord3 = board[cord3[0]][cord3[1]]

        if ((item_cord1 != " " and item_cord1 and item_cord2 and item_cord3) and 
            item_cord1 == item_cord2  == item_cord3):
            if item_cord1 == 'X':
                x_wins = True
            elif item_cord1 == 'O':
                o_wins = True        

    if x_wins and o_wins:
        raise ValueError("Impossible board: game should have ended after the game was won")
        
    if x_wins or o_wins:
        return "win"
    
    if occupied_boxes == 9:
        return "draw"
    
    if occupied_boxes == 9:
        return "draw"

    return "ongoing"

Syntax Notes

• The code counts X and O marks first so it can reject invalid turn order early.
• The win_boxes list enumerates every row, column, and diagonal to check.
• Each route is compared against the board to see whether all three cells match.
• A game is a win if either player completes a line, but not both.
• A full board with no winner is a draw; otherwise the game is ongoing.