Question

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

  • Method 1：　Design 
    class TicTacToe {
    private int[][] pad;
    private int n;
    /** Initialize your data structure here. */
    public TicTacToe(int n) {
        this.pad = new int[n][n];
        this.n = 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) {
        this.pad[row][col] = player;
        if(checkHorizontal(row, col, player) || checkVertical(row, col, player) || checkDiagonal(row, col, player)){
            return player;
        }
        return 0;
    }
    private boolean checkHorizontal(int row, int col, int player){
        int ty = col;
        while(ty >= 0){
            if(pad[row][ty--] != player) return false;
        }
        ty = col;
        while(ty < n){
            if(pad[row][ty++] != player) return false;
        }
        return true;
    }
    private boolean checkVertical(int row, int col, int player){
        int tx = row;
        while(tx >= 0){
            if(pad[tx--][col] != player) return false;
        }
        tx = row;
        while(tx < n){
            if(pad[tx++][col] != player) return false;
        }
        return true;
    }
    private boolean checkDiagonal(int row, int col, int player){
        int tx = 0, ty = 0;
        boolean res0 = true;
        while(tx < n && ty < n){
            if(pad[tx++][ty++] != player){
                res0 = false;
                break;
            }
        }
        boolean res1 = true;
        tx = n - 1;
        ty = 0;
        while(tx >= 0 && ty < n){
            if(pad[tx--][ty++] != player){
                res1 = false;
                break;
            }
        }
        return res0 || res1;
    }
}

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