How to Fill a 2D Array Diagonally in Java Without Using Math.abs

Learn how to create a n×n matrix in Java and fill it diagonally without using the `abs` function. This guide provides a step-by-step approach to solving the problem for beginners.
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The Problem

The goal is to fill an n×n matrix such that:

The primary diagonal (from the top-left to the bottom-right) contains zeros.

The diagonals adjacent to the primary diagonal contain the number one, and so forth.

The maximum size of the matrix can be 100.

Example Output for n = 5:

[[See Video to Reveal this Text or Code Snippet]]

Understanding the Matrix Layout

Before jumping into coding, let’s visually break down the structure of the matrix. For a 5x5 matrix, it looks like this:

The indices where the value is 0 are where i == j (the primary diagonal).

Adjacent values (1) appear when j is one unit away from i (both above and below the diagonal).

The number increases as you move further away from the diagonal.

The Solution Approach

Step 1: Initialize the Matrix

Create a matrix of size n×n. For this guide, we'll set n to 5 for clarity, but it can be any number up to 100.

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Fill the Matrix

Using nested loops, we can traverse each element in the matrix.

Outer Loop (i) iterates through the rows.

Inner Loop (j) iterates through the columns.

For each position (i, j):

Set the value to 0 if i == j (the primary diagonal).

If j < i, set the value to an incrementing value based on the previous row's value; essentially, you can build on the value of the previous row's element.

If j > i, calculate the difference between j and i to obtain the correct value.

Here’s the corresponding code for these steps:

[[See Video to Reveal this Text or Code Snippet]]

Step 3: Display the Matrix

After filling the array, you need to print it to verify the correctness of the entries.

[[See Video to Reveal this Text or Code Snippet]]

Full Code Example

Here’s the complete code that implements the above logic:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

Filling a 2D array diagonally in Java can be an enlightening exercise. It helps you understand the mechanics of array indexing and nested loops. With this approach, you can easily adjust for any size of the matrix, so long as it does not exceed 100. Happy coding!