Complete DFS-1

[PrakarshKamal]

No description provided.

[super30admin]

Flood Fill the image (FloodFill.java)

Your solution is correct and well-implemented. Both BFS and DFS are valid approaches for flood fill. Here are some points for improvement:

1. Parameter Passing in DFS: In the DFS method, you are passing several parameters (n, m, dirs, oldColor, color) that remain constant throughout the recursion. This can be optimized by making them instance variables or fields of the class, or by using a helper function that captures these constants (e.g., using a closure in Java 8+ with lambda, but note that Java lambdas require final or effectively final variables). Alternatively, you can define these constants inside the method and use an inner method (if using Java 16+ for local methods) or simply avoid passing them repeatedly. For example, you can compute oldColor once in floodFill and then use it in DFS without passing it every time. Similarly, dirs can be defined as a static final array if it doesn't change.

2. Recursion vs Iteration: While DFS recursion is acceptable for this problem due to the constraints, be aware that for larger grids it might cause stack overflow. The BFS approach (which you have commented) is iterative and avoids deep recursion. You might consider using iterative DFS with a stack if you prefer DFS without recursion. However, both are correct.

3. Code Duplication: You have two implementations (BFS and DFS) in the same file, which is good for learning, but in practice, you should choose one. The problem doesn't require a specific method, so either is fine.

4. Style: The code is readable and well-indented. However, you could add a comment explaining why you return immediately if oldColor == color (to avoid infinite recursion or unnecessary processing). Also, consider making dirs a static final array since it is constant.

Example improvement for DFS (without passing constant parameters):

class Solution {
    private static final int[][] DIRS = {{0,1}, {1,0}, {-1,0}, {0,-1}};
    
    public int[][] floodFill(int[][] image, int sr, int sc, int color) {
        int oldColor = image[sr][sc];
        if (oldColor == color) return image;
        int n = image.length, m = image[0].length;
        dfs(image, sr, sc, n, m, oldColor, color);
        return image;
    }
    
    private void dfs(int[][] image, int i, int j, int n, int m, int oldColor, int color) {
        if (i < 0 || j < 0 || i >= n || j >= m || image[i][j] != oldColor) return;
        image[i][j] = color;
        for (int[] dir : DIRS) {
            dfs(image, i + dir[0], j + dir[1], n, m, oldColor, color);
        }
    }
}

Note: In this version, DIRS is a constant, and we check the condition inside the DFS method to avoid passing the same parameters. Also, we check the condition at the beginning of DFS to make the code more concise.

Overall, your solution is correct and efficient. Good job!

VERDICT: PASS

---

Nearest zero (01Matrix.java)

Your solution is well-implemented and follows the standard BFS approach for this problem. Here are some strengths and suggestions:

Strengths:

• Correct use of BFS from multiple sources (all zeros) to efficiently compute distances.
• Good handling of boundaries with condition checks.
• Clear variable names and comments that make the code readable.

Areas for Improvement:

• The direction array order: While it doesn't affect correctness, it's common to list all four directions symmetrically (e.g., up, down, left, right). The order in your code is acceptable, but for consistency, you might consider using a more standard order like {{-1,0}, {1,0}, {0,-1}, {0,1}}.
• Instead of using a distance counter that increments each level, you could set the distance for a neighbor as mat[curr[0]][curr[1]] + 1 if you stored the distances in the matrix. However, your current approach is correct and clear.

Minor Note:

• You use n for rows and m for columns, which is fine, but ensure consistency with problem statements to avoid confusion. The problem uses m for rows and n for columns, but your variable naming is clear within the context.

Overall, excellent job!

VERDICT: PASS