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  1. #1
    Propinquity is offline Member
    Join Date
    Oct 2013
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    Default Can someone explain this method to me?

    This was proposed as a possible solution for determining checks in tic-tac-toe.
    I don't think I really understand why it works, how they could have possibly come up with this, or the math behind it.
    In my program, the best I came up with was to brute force check systematically against a list of solutions that I had compiled.

    I understand that the method works by checking the row and column coordinates of the last move made, and seeing if that move caused the player to win.
    I don't understand why "(row ==col)||(col== -1* row+ (board.length-1));" would allow the program to know that it is on a diagonal, though. Along with the other if statements in the method.

    Java Code:
     public boolean isWinner(int row, int col){
    	 String Player = Character.toString(board[row][col]);
    	 boolean onDiagonal = (row ==col)||(col== -1* row+ (board.length-1));
    	 boolean HorizontalWin = true; 
    	 boolean VerticalWin = true;
    	 boolean DiagonalWinOne = true; 
    	 boolean DiagonalWinTwo = true;
    	for (int n = 0; n<board.length; n++){ //Checks rows and columns
    			HorizontalWin = false;
    			VerticalWin = false;
    	if(onDiagonal){ /*this check only passes if the move was a diagonal. if the move
    		was not a diagonal, then the method would have already returned.*/
    		for(int n = 0; n < board.length; n++){
    				DiagonalWinOne = false;
    				DiagonalWinTwo = false;
    		DiagonalWinOne = false;
    		DiagonalWinTwo = false;
    	boolean hasWon = (HorizontalWin || VerticalWin || DiagonalWinOne || DiagonalWinTwo);
    	return hasWon;

  2. #2
    jim829 is offline Senior Member
    Join Date
    Jan 2013
    Northern Virginia, United States
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    Default Re: Can someone explain this method to me?

    There are only five places which can be on a diagonal. The first part is obvious (row=0, col=0, row=1, col=1, or row=2, col=2). The expression you question, IMHO, is poorly written. Try it this way and work it out on paper.

    Java Code:
    boolean onDiagonal = (row ==col)||(col== (board.length-row-1);
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