348.Design Tic-Tac-Toe

348.Design Tic-Tac-Toe

Assume the following rules are for the tic-tac-toe game on an n x n board between two players:

A move is guaranteed to be valid and is placed on an empty block.
Once a winning condition is reached, no more moves are allowed.
A player who succeeds in placing n of their marks in a horizontal, vertical, or diagonal row wins the game.
Implement the TicTacToe class:

- TicTacToe(int n) Initializes the object the size of the board n.
- int move(int row, int col, int player) Indicates that the player with id player plays at the cell (row, col) 
of the board. The move is guaranteed to be a valid move, and the two players alternate in making moves. Return
    - 0 if there is no winner after the move,
    - 1 if player 1 is the winner after the move, or
    - 2 if player 2 is the winner after the move.

Difficulty : Medium

Solution

This is a problem where we can use the concept of rows, columns, and diagonals to keep track of the current
player’s marks. In an nxn TicTacToe board, a player wins if they have n marks on any row, column or diagonal.

We can create four integer arrays: rows, columns, and two diagonals.
Player1 will +1 to the position, and player2 will -1.
When any position reaches n or -n, that means player1 or player2 wins.

public class TicTacToe {
    private int[] rows;
    private int[] cols;
    private int diagonal;
    private int antiDiagonal;

    /** Initialize your data structure here. */
    public TicTacToe(int n) {
        rows = new int[n];
        cols = new int[n];
    }
    
    /**
     * Player {player} makes a move at ({row}, {col}).
     *
     * @param row    The row of the board.
     * @param col    The column of the board.
     * @param player The player, can be either 1 or 2.
     * @return The current winning condition, can be either:
     * 0: No one wins.
     * 1: Player 1 wins.
     * 2: Player 2 wins.
     */
    public int move(int row, int col, int player) {
        int toAdd = player == 1 ? 1 : -1;

        rows[row] += toAdd;
        cols[col] += toAdd;
        if (row == col)
        {
            diagonal += toAdd;
        }

        if (col == (cols.length - row - 1))
        {
            antiDiagonal += toAdd;
        }

        int size = rows.length;
        if (Math.abs(rows[row]) == size ||
            Math.abs(cols[col]) == size ||
            Math.abs(diagonal) == size  ||
            Math.abs(antiDiagonal) == size)
        {
            return player;
        }

        return 0;
    }
}