Hashing 2:Completed 3 problems

[raninagare]

No description provided.

[super30admin]

Subarray Sum Equals K (SubArraySumK.java)

Strengths:

• Your solution is correct and uses the optimal approach for this problem
• Excellent comments that explain the mathematical reasoning behind the algorithm — this shows deep understanding
• Clean variable naming and logical structure
• Proper handling of the edge case (initial (0, 1) entry in the map)

Areas for Improvement:

1. Simplify the map update: Replace your three-line map update with a single line using getOrDefault:

   map.put(rSum, map.getOrDefault(rSum, 0) + 1);

   This is more concise, idiomatic Java, and slightly more efficient.

2. Class naming convention: For LeetCode submissions, the class is typically expected to be named Solution. While your naming is descriptive, it may cause submission issues on the platform.

3. Consider using HashMap directly: Since you don't need ordering or any special Map features, declaring the variable as HashMap<Integer, Integer> (rather than Map<Integer, Integer>) is fine and slightly more explicit about the implementation choice.

4. Minor style: The comment block at the top is good practice for documenting complexity and approach — keep doing this!

VERDICT: PASS

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Contiguous Array (ContinuousSubArray.java)

The student's solution is essentially identical to the reference solution in terms of approach and implementation. Let me analyze each criterion:

1. Correctness: The solution correctly solves the problem. It uses the running sum pattern where:

   • 0 decrements the running sum by 1
   • 1 increments the running sum by 1
   • If two indices have the same running sum, the subarray between them is balanced (equal 0s and 1s)
   • The initial entry of (0, -1) handles the edge case where the balanced subarray starts from index 0
   • The solution correctly tracks the maximum length

2. Time Complexity: O(n) - matches the reference solution. Single pass through the array.

3. Space Complexity: O(n) - matches the reference solution. Uses a HashMap to store running sums.

4. Code Quality:

   • The code is well-structured and readable
   • Good comments explaining the approach
   • The class name is slightly different ("ContinuousSubArray" vs "Solution") but this is acceptable
   • The comments at the top provide a clear explanation of the approach
   • The logic flow is clear

5. Eiviency: The solution is optimal. No further optimizations needed.

The student's solution is functionally identical to the reference solution with the same approach, time complexity, and space complexity.

FEEDik:
Your solution is excellent! It correctly implements the optimal approach for this problem. Here are some observations:

Strengths:

• Correctly identified and implemented the running sum pattern
• Properly handled the edge case by initializing the map with (0, -1)
• Clean, readable code with helpful comments
• Optimal time and space complexity
• Good explanation of the approach in the comments

Minor suggestions for improvement:

• Consider adding more inline comments to explain specific parts of the logic (e.g., why we decrement for 0 and increment for 1)
• The class name "ContinuousSubArray" differs from the typical "Solution" naming convention used in LeetCode, but this is a minor stylistic point
• You could add a brief explanation of why the running sum approach works (equal 0s and 1s means the sum returns to the same value)

Overall: This is a well-implemented solution that demonstrates a strong understanding of the problem and the optimal approach. Great work!

VERDICT: PASS

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Longest Palindrome (LongestPalindrome.java)

Your solution is correct and well-structured! Here are some observations:

Strengths:

• Correct logic that matches the reference solution
• Good time complexity O(n) and space complexity O(1)
• Nice comments explaining the approach
• Proper handling of edge cases (null/empty string)
• Clean and readable code

Minor suggestions:

• Consider using Set<Character> with explicit type parameter for better readability: Set<Character> set = new HashSet<>();
• The class name should ideally be Solution to match the expected interface, though this depends on the platform
• You could use enhanced for loop for cleaner iteration: for (char ch : s.toCharArray())

Overall, this is a solid solution that demonstrates good understanding of the problem.

VERDICT: PASS