DP-2 Solution

[Simranb10]

No description provided.

[super30admin]

Paint House (PaintHouse.java)

Strengths:

• Excellent use of dynamic programming to achieve O(n) time complexity, which is optimal for this problem
• Clean and readable code structure with clear variable naming
• Correct base case initialization for all three colors
• Proper handling of the adjacency constraint through the min() logic

Areas for Improvement:

• Space optimization: The solution uses O(n) space with a 2D array, but this can be reduced to O(1) by only keeping track of the previous row's values. This is a common optimization for this classic DP problem.
• Could add comments explaining the DP recurrence relation for better documentation

VERDICT: PASS

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Coin Change II (CoinChange2.java)

Strengths:

• Good attempt at using dynamic programming, which is a significant improvement over the recursive reference solution
• Correctly identified the time complexity as polynomial
• Code structure is relatively clean

Areas for Improvement:

• Critical Bug: The initialization comb[i][amount] = 1; is incorrect. It should be comb[i][0] = 1; to represent the base case of making amount 0
• Logic Error: When iterating backwards (amt >= 0), accessing comb[i][amt + coins[i]] will cause index out of bounds errors. The DP recurrence needs to be reconsidered
• Space Optimization: Consider using a 1D array dp[amount+1] where dp[amt] represents the number of ways to make amount amt. This reduces space from O(n * amount) to O(amount)
• Comments: Add comments explaining the DP state and recurrence relation
• Variable Naming: Use more descriptive names like dp instead of comb, and coinIndex/currentAmount for clarity

Correct DP Approach Hint: For this problem, you should iterate coins in outer loop and amounts in inner loop (ascending), using: dp[amt] += dp[amt - coin]

VERDICT: NEEDS_IMPROVEMENT