Completed Precourse - 2

[yashhh-23]

No description provided.

[Copilot]

Pull request overview

Note

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Adds completed implementations for several algorithm exercises (binary search, quicksort, mergesort, linked-list middle) and introduces an iterative quicksort solution while removing an unused placeholder file.

Changes:

• Implemented recursive binary search and quicksort, plus iterative quicksort using an explicit stack.
• Implemented fast/slow pointer middle-element printing for a singly linked list.
• Partially implemented merge sort (merge + recursive sort), and removed the old Exercise_5 stub.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
IterativeQuickSort.java	New iterative quicksort implementation and runnable demo
Exercise_5.java	Removed placeholder / incomplete quicksort stub
Exercise_4.java	Added merge sort implementation (merge + recursive sort)
Exercise_3.java	Implemented printMiddle using fast/slow pointers
Exercise_2.java	Implemented quicksort swap/partition/sort
Exercise_1.java	Implemented recursive binary search

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[super30admin]

Let me evaluate each file in the student's solution:

1. BInarySearch.java

• Correctness: The binary search implementation is correct. It properly handles the base case (r >= l), calculates the mid-point without overflow, and correctly narrows down the search space based on comparison with the target element.
• Time Complexity: O(log n) - correct
• Space Complexity: O(log n) due to recursive calls (stack space). The comment says O(1) which is incorrect.
• Code Quality: Good structure, readable, follows standard binary search pattern.

2. IterativeQuickSort.java

• Correctness: The iterative quick sort using a stack is correctly implemented. The partition logic is correct, and the stack-based approach properly handles the subarrays.
• Time Complexity: O(n log n) average, O(n²) worst case - correct
• Space Complexity: O(log n) for the stack in average case, but worst case can be O(n). The comment is partially correct.
• Code Quality: Good implementation with clear comments. The swap without extra variable is clever but could potentially overflow for large integers.

3. MergeSort.java

• Correcting: The merge sort implementation is correct. The merge function properly merges two sorted subarrays, and the sort function recursively divides the array.
• Time Complexity: O(n log n) - correct
• Space Complexity: O(n) for the temporary arrays L and R created during merge. The comment says O(log n) which is incorrect.
• Space Complexity: The merge sort requires O(n) auxiliary space for the temporary arrays. The comment is incorrect.
• Code Quality: Well-structured with clear separation of concerns. The merge function is correctly implemented.

4. QuickSort.java

• Correctness: The recursive quick sort implementation is correct. The partition function correctly places the pivot at its correct position.
• Time Complexity: O(n log n) average, O(n²) worst case - correct
• Space Complexity: O(log n) due to recursion stack in average case, O(n) in worst case. The comment is reasonable.
• Code Quality: Clean implementation with good structure.

5. SinglyLL.java

• Correctness: The middle element detection using fast and slow pointers is correctly implemented. It handles the edge case where head is null.
• Time Complexity: O(n) - correct
• Space Complexity: O(1) - correct
• Code Quality: Good use of the fast and slow pointer technique.

Overall Assessment:

• All algorithms are correctly implemented and follow standard patterns.
• The main issue is with the space complexity comments - several are inaccurate.
• The swap without extra variable in IterativeQuickSort.java could cause integer overflow for large values.
• Code structure and readability are generally good across all files.