Complete Linked-List 1

[paridhimalviya]

Problem1 (https://leetcode.com/problems/reverse-linked-list/)

Problem2 (https://leetcode.com/problems/remove-nth-node-from-end-of-list/)

Problem3 (https://leetcode.com/problems/linked-list-cycle-ii/)

[super30admin]

Strengths:

• You have implemented both iterative and recursive solutions, which shows a good understanding of different approaches.
• The iterative solution is efficient and matches the reference solution in time and space complexity.
• You have explored multiple recursive methods, which is good for learning.

Areas for Improvement:

1. Avoid redefining the ListNode class. Use the one provided by the problem to prevent conflicts.
2. For recursive solutions, avoid using instance variables (like result and newHead) to store the result. This introduces state and makes the function non-reentrant. Instead, use pure recursion that returns the result directly (as in reverseUsingNodeReturnType).
3. The method reverseListByRecursionUsingPointers uses a helper function that modifies instance state. This can be refactored to be purely recursive without state. For example, you can implement recursion by passing the previous node as a parameter and returning the new head.
4. The method reverseUsingRecursionStack is implemented correctly in terms of logic, but using an instance variable is not ideal. Instead, you can return the new head from the recursive function.
5. Consider adding comments to explain each approach, especially since the problem asks for both iterative and recursive solutions. This will make your code more readable.
6. Ensure that your solution file only contains code relevant to the problem. The other files (like CyclicLinkedList and RemoveNthNodeFromEnd) are separate problems and should not be included in the same evaluation.

Here is a refined version of your recursive solution without instance variables:

// Recursive solution without instance variables
func reverseListRecursive(_ head: ListNode?) -> ListNode? {
    if head == nil || head?.next == nil {
        return head
    }
    let newHead = reverseListRecursive(head?.next)
    head?.next?.next = head
    head?.next = nil
    return newHead
}

This is concise and efficient (though still O(n) space due to recursion).

[super30admin]

Strengths:

• You have attempted multiple approaches (iterative and recursive) to solve the problem, which shows a good understanding of the problem and different techniques.
• The iterative solution is correct and efficient.

Areas for Improvement:

• Avoid using global variables (like result and newHead) in recursive functions. Instead, use the return value to propagate the new head. The method reverseListUsingNodeReturnType is a good example of this.
• Ensure that all methods are correctly implemented. For instance, the method reverseUsingRecursionStack does not set result and returns it, which will always be nil. Also, the helper function reverse in reverseListByRecursionUsingPointers does not update the prev parameter correctly because Swift parameters are passed by value. You should use in-out parameters or redesign the function.
• Be consistent with the node type. The problem expects a ListNode class, but your code uses both ListNode and LLNode<Int>. This might cause compilation errors. Stick to the node type defined in the problem.
• For the recursive approach, the standard method without helper parameters (like reverseListUsingNodeReturnType) is cleaner and should be preferred over methods that use global state.
• Test your code thoroughly for edge cases (empty list, single node list) to ensure all methods work correctly.

Overall, your iterative solution is excellent. Focus on improving the recursive implementations by avoiding global state and using proper parameter passing.