adding an array table (bidimensional) to a List (Java)-CodePudding

I am doing a Bingo program and now, the section of the bingoCard, to do this I am using an a bidimensional array but I need to shuffle the numbers of each row. For the shuffle part I saw that the setList is much better, but I don't know how to relate the List with the array here is a part of the code:

public static Integer[][] bingoCard(){
    Integer [][] bingoCard= new Integer[3][9];
    for(int x =0; x<bingoCard.length; x  ){
        for(int y =0; y<bingoCard[x].length; y  ){
            if(y <5){
                int random = (int)(Math.random()*90 1);
                System.out.print((bingoCard[0][y] = random)   " ");
            }
            if(y >4 && y <9){
                System.out.print((bingoCard[0][y] = 0)   " ");
            }
        } 
        System.out.println();           
    } 
    List<Integer[]> list =Arrays.asList(bingoCard);
    Collections.shuffle(list);
    list.toArray(bingoCard);    
    return bingoCard;
}

Any question please ask me!! Thanks.

CodePudding user response：

In your code, when you do List<Integer[]> list = Arrays.asList(bingoCard), you are converting the outer array into a List and then shuffling its contents. The effect of this will be that the order of the 3 rows are shuffled rather than the contents of the 3 rows which is what you want. You could achieve this by shuffling the contents of each row within your for-loop. Or, after constructing the 2D array, you can loop over each row again and shuffle them.

Also, you have another small bug. When you assign the value, you are doing bingoCard[0][y] = ... but it should be bingoCard[x][y]. Otherwise, you are only assigning the first row new values on each iteration.

I would recommend not converting the array to a List just to shuffle it and then converting it back. Instead, you can use Random.nextInt to pick indexes of the array to assign. That would look something like this:

public static Integer[][] bingoCard(){
    int numRows = 3;
    int numCols = 9;
    int randomNumbersPerRow = 5;
    int randomNumberBound = 90;

    Random random = new Random();
    Integer[][] bingoCard = new Integer[numRows][numCols];
    for (int row = 0; row < numRows; row  ) {
        for (int col = 0; col < numCols; col  ) {
            // Initialize all spots to 0
            bingoCard[row][col] = 0;
        }
        for (int i = 0; i < randomNumbersPerRow; i  ) {
            // Choose a spot to assign a random number
            int indexToAssign = random.nextInt(numCols);
            // Make sure we haven't already chosen it
            while (bingoCard[row][indexToAssign] != 0) {
                indexToAssign = random.nextInt(numCols);
            }
            int numToAssign = random.nextInt(randomNumberBound)   1;
            bingoCard[row][indexToAssign] = numToAssign;
        }
    }

    // Print the bingo card
    for (int row = 0; row < numRows; row  ) {
        for (int col = 0; col < numCols; col  ) {
            System.out.printf("- ", bingoCard[row][col]);
        }
        System.out.println();
    }
    return bingoCard;
}