completed DP-3

[yashhh-23]

No description provided.

[super30admin]

Least Falling Path Sum (deleteearn.java)

Looking at this evaluation, I need to assess the student's solution against the problem requirements.

Analysis

Problem: Least Falling Path Sum - Given an n x n matrix, find the minimum sum of any falling path starting from any element in the first row, where each step moves to the next row either directly below, diagonally left, or diagonally right.

Student's Solution: The student submitted a solution for "Delete and Earn" problem, which is a completely different problem (LeetCode 740). Their code:

• Takes an array of numbers
• Transforms it to count frequency × value for each number
• Uses DP with memoization to maximize points by "deleting and earning"
• Has nothing to do with matrix falling paths

Evaluation

1. Correctness: ❌ FAIL - The solution solves the wrong problem entirely. It doesn't address falling paths in a matrix, doesn't use the input format matrix[][], and implements a completely different algorithm for "Delete and Earn".

2. Time Complexity: N/A - Not applicable since it's solving the wrong problem.

3. Space Complexity: N/A - Not applicable since it's solving the wrong problem.

4. Code Quality: The code itself is well-structured with:

• Good variable naming
• Clear comments
• Proper memoization implementation
• Clean helper function structure

However, it's solving the wrong problem.

5. Efficiency: N/A - Not applicable.

---

Feedback

Strengths:

• The code demonstrates solid understanding of memoization and DP
• Good coding practices with comments and clear variable names
• Correct handling of edge cases (empty input)
• Efficient transformation of input (O(n) to build frequency array)

Critical Issues:

• Wrong Problem: This is the most serious issue. The solution solves "Delete and Earn" (LeetCode 740), not "Least Falling Path Sum" (LeetCode 931)
• Wrong Input Handling: The solution expects a 1D array but the problem requires a 2D matrix
• Wrong Algorithm: The falling path problem requires considering 3 possible moves (down, down-left, down-right), not 2 options
• No Matrix Traversal: The solution never processes matrix rows/columns

---

The student needs to:

1. Re-read the problem statement carefully
2. Implement a solution that handles a 2D matrix input
3. Use dynamic programming where each cell considers values from cells directly below, below-left, and below-right
4. Start from the last row and work upward (bottom-up DP) or use top-down with memoization for each position

VERDICT: NEEDS_IMPROVEMENT

---

Delete and Earn (minpath.java)

Looking at this evaluation, I need to assess the student's solution for the "Delete and Earn" problem.

Problem Mismatch Analysis

The student submitted a solution for "Minimum Falling Path Sum" (LeetCode 931), but the assigned problem is "Delete and Earn" (LeetCode 740).

The student's solution:

• Takes a 2D matrix as input
• Finds minimum sum falling path through the matrix
• This is completely different from the Delete and Earn problem

Evaluation

1. Correctness: ❌ FAIL

• The solution solves the wrong problem entirely
• It doesn't address the Delete and Earn requirements at all
• Cannot earn any points as it operates on a completely different algorithm

2. Time Complexity: ❌ INAPPLICABLE

• O(n²) is irrelevant since the wrong problem is being solved
• The reference solution achieves O(n + max_val) which is optimal

3. Space Complexity: ✅ GOOD (for the wrong problem)

• O(1) space by modifying matrix in-place (good for Minimum Falling Path Sum)

4. Code Quality: ✅ GOOD (for the wrong problem)

• Well-structured with clear comments
• Proper variable naming
• Good use of Math.min comparisons

5. Efficiency: ✅ GOOD (for the wrong problem)

• Efficiently handles edge cases (c > 0, c < n-1)
• In-place modification saves space

Feedback

Strengths:

• The code is well-structured and readable
• Comments are clear and explain the approach
• Handles boundary conditions properly
• Good space optimization by modifying matrix in-place

Critical Issue:

• This is the wrong problem entirely. The submitted solution addresses "Minimum Falling Path Sum" not "Delete and Earn". The student needs to implement the correct algorithm.

For Delete and Earn, the approach should be:

1. Count occurrences of each number and calculate total points per value
2. Apply a House Robber DP pattern where selecting value i means you cannot select i-1
3. dp[i] = max(dp[i-1], arr[i] + dp[i-2])

VERDICT: NEEDS_IMPROVEMENT