Question

Hi I am trying to create a matrix on the console using 2D array. The idea is that the output should look like this one :

1|8|9 |16
2|7|10|15
3|6|11|14
4|5|12|13

Is there any one who has an idea how it can be done?

Answer 1

Few things you can guess from the matrix: –

• First, you have to traverse all rows of a columns first before moving to the next column

• Second, you need to alternate between downwards and upwards direction on each iteration

• So, you would need two nested for loop, for iterating through rows for a particular column. One will go from row 0 to max - 1, and the next will go from row = max - 1 to 0.

• Now, to alternate the iteration direction, you can use a boolean variable, and toggle it after each iteration of inner loop finishes.

• Each loop needs to be enclosed inside an if-else. Both of them will be executed on a certain condition. If boolean downwards = false;, then loop moving upwards will be executed and vice-versa.

• On each iteration, fill the current cell with an integer counter, that you would have to initialize with 1, and increment it after each fill.

---

Pseudo code : –

    // Initialize variables row, col, and count = 1

    boolean goDown = true;

    int[][] matrix = new int[row][col];  // declare matrix

    for i = 0 to col:
        if (goDown)
            for j = 0 to row:  // Move in downwards direction
                assign count++ to matrix[j][i] 
                // assign to `[j][i]` because, we have to assign to rows first

            goDown = false;    // Toggle goDown

        else
            for j = row - 1 to 0:  // Move in upwards direction
                assign count++ to matrix[j][i] 

            goDown = true;  // toggle goDown

    }