Design Tic-Tac-Toe

Design a Tic-tac-toe game that is played between two players on a n x n grid.

You may assume the following rules:

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

Example:

Given n = 3, assume that player 1 is "X" and player 2 is "O" in the board.

TicTacToe toe = new TicTacToe(3);

toe.move(0, 0, 1); -> Returns 0 (no one wins) |X| | | | | | | // Player 1 makes a move at (0, 0). | | | |

toe.move(0, 2, 2); -> Returns 0 (no one wins) |X| |O| | | | | // Player 2 makes a move at (0, 2). | | | |

toe.move(2, 2, 1); -> Returns 0 (no one wins) |X| |O| | | | | // Player 1 makes a move at (2, 2). | | |X|

toe.move(1, 1, 2); -> Returns 0 (no one wins) |X| |O| | |O| | // Player 2 makes a move at (1, 1). | | |X|

toe.move(2, 0, 1); -> Returns 0 (no one wins) |X| |O| | |O| | // Player 1 makes a move at (2, 0). |X| |X|

toe.move(1, 0, 2); -> Returns 0 (no one wins) |X| |O| |O|O| | // Player 2 makes a move at (1, 0). |X| |X|

toe.move(2, 1, 1); -> Returns 1 (player 1 wins) |X| |O| |O|O| | // Player 1 makes a move at (2, 1). |X|X|X|

Follow up: Could you do better than O(n2) per move() operation?

Solution

public class TicTacToe {
  int[] rows;
    int[] columns;
    int cross1;
    int cross2;
    int size;

    public TicTacToe(int n) {
        rows = new int[n];
        columns = new int[n];
        cross1 = 0;
        cross2 = 0;
        size = 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 addtion = player == 1 ? 1 : -1;
        rows[row] += addtion;
        columns[col] += addtion;

        if (row == col) {
            cross1 += addtion;
        }

        if (row + col == size - 1) {
            cross2 += addtion;
        }

        if (Math.abs(rows[row]) == size || Math.abs(columns[col]) == size || Math.abs(cross1) == size || Math.abs(cross2) == size) {
            return player == 1 ? 1 : 2;
        }

        return 0;
    }
}

/**
 * Your TicTacToe object will be instantiated and called as such:
 * TicTacToe obj = new TicTacToe(n);
 * int param_1 = obj.move(row,col,player);
 */