add two-pointer solutions

[nikhylw]

No description provided.

[super30admin]

Merging of 2 arrays (remove_duplicates_sortarr.py)

The student appears to have submitted code for the wrong problem. The submitted solution addresses "Remove Duplicates from Sorted Array II" (keeping at most 2 duplicates), while the problem statement clearly asks for "Merging of 2 arrays" where two sorted arrays need to be merged into one sorted array in-place.

If the student intended to solve the merge problem, they should implement a solution that:

• Uses three pointers: one for nums1's valid elements, one for nums2, and one for placing elements from the back
• Merges from the end to avoid overwriting unprocessed elements
• Handles edge cases where one array is exhausted

The code quality for the wrong problem is actually quite good - it's clean, well-structured, and efficient. However, it does not address the given problem at all.

VERDICT: NEEDS_IMPROVEMENT

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Search 2D sorted matrix II (search_in_2d_matrix.py)

Strengths:

1. Excellent optimization - by first identifying the correct row, the solution achieves O(m + log n) instead of O(m log n)
2. Clean implementation with proper binary search implementation (using low + (high - low) // 2 to prevent overflow)
3. Good edge case handling (when no row has last element >= target)
4. Well-documented time and space complexity in comments

Areas for Improvement:

1. The solution assumes the matrix is non-empty (which is valid per constraints, but could add a defensive check)
2. Could consider the alternative "staircase" approach starting from top-right corner, which is O(m + n) worst case

Minor suggestions:

• Consider adding type hints for better code documentation
• The solution is already quite optimal; the approach is sound

VERDICT: PASS

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Edit and Remove Duplicates in an array

For remove_duplicates_sortarr.py:

• Strength: Good attempt at a two-pointer approach with O(1) space
• Weakness: The comparison logic nums[slow - k] doesn't properly track duplicate counts
• The condition should track how many times the current element has been seen, not just compare with an element k positions back
• Consider using a counter variable like the reference solution to track occurrences

For search_in_2d_matrix.py:

• Strength: Excellent implementation with clear logic flow
• The row-finding + binary search combination is optimal
• Well-structured with good variable naming
• Handles edge cases correctly (row == -1 check)

VERDICT: NEEDS_IMPROVEMENT