Create SpiralOrderMatrix.java

[o10a19]

Summary by Sourcery

New Features:

• Implement a method to generate an n x n matrix filled with numbers in spiral order.

[sourcery-ai]

Reviewer's Guide by Sourcery

This PR introduces a new class Solution with a method generateMatrix that creates an n×n matrix filled with numbers from 1 to n² in a spiral order pattern. The implementation uses a boundary-tracking approach to traverse the matrix in a spiral pattern, first populating a 2D array and then converting it to the required ArrayList format.

No diagrams generated as the changes look simple and do not need a visual representation.

File-Level Changes

Change	Details	Files
Implementation of spiral matrix generation using boundary tracking	Defines four boundaries (top, bottom, left, right) to track the current spiral position Uses a counter variable to fill numbers from 1 to n² Implements four directional traversals: left-to-right, top-to-bottom, right-to-left, and bottom-to-top Updates boundary variables after each directional traversal	Java/SpiralOrderMatrix.java
Array to ArrayList conversion logic	Creates a nested ArrayList structure to match the required return type Converts the populated 2D array into ArrayList<ArrayList> format Implements row-by-row conversion using nested loops	Java/SpiralOrderMatrix.java

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[sourcery-ai]

Hey @o10a19 - I've reviewed your changes - here's some feedback:

Overall Comments:

• Consider building the ArrayList directly instead of creating an array first and converting it. This would improve both memory usage and performance.
• Add input validation to handle invalid cases (e.g., negative numbers) at the start of the method.

Here's what I looked at during the review

• 🟡 General issues: 1 issue found
• 🟢 Security: all looks good
• 🟢 Testing: all looks good
• 🟡 Complexity: 1 issue found
• 🟢 Documentation: all looks good

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[sourcery-ai]

issue: Add input validation for parameter 'n' to handle negative values

The method should throw an IllegalArgumentException when n < 0 to prevent array allocation issues

[sourcery-ai]

issue (complexity): Consider directly building the ArrayList during spiral traversal instead of using an intermediate array

The code can be simplified by directly building the ArrayList<ArrayList> during spiral traversal, eliminating the need for conversion between data structures. This reduces both memory usage and code complexity:

public ArrayList<ArrayList<Integer>> generateMatrix(int n) {
    ArrayList<ArrayList<Integer>> matrix = new ArrayList<>();
    // Initialize the matrix with n rows of n elements
    for (int i = 0; i < n; i++) {
        ArrayList<Integer> row = new ArrayList<>();
        for (int j = 0; j < n; j++) {
            row.add(0);
        }
        matrix.add(row);
    }

    int top = 0, bottom = n - 1, left = 0, right = n - 1;
    int counter = 1;

    while (counter <= n * n) {
        for (int i = left; i <= right; i++)
            matrix.get(top).set(i, counter++);
        top++;

        for (int i = top; i <= bottom; i++)
            matrix.get(i).set(right, counter++);
        right--;

        for (int i = right; i >= left; i--)
            matrix.get(bottom).set(i, counter++);
        bottom--;

        for (int i = bottom; i >= top; i--)
            matrix.get(i).set(left, counter++);
        left++;
    }

    return matrix;
}

This version:

1. Creates the ArrayList structure once
2. Eliminates the need for conversion
3. Uses less memory by avoiding duplicate data structures
4. Maintains the same spiral traversal logic but with direct ArrayList operations