[chjung99] WEEK 01 solutions

[chjung99]

답안 제출 문제

• Two Sum #219
• Valid Parentheses #222
• Merge Two Sorted Lists #224
• Climbing Stairs #230
• Same Tree #228

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[chjung99]

Week 설정 추가

[chjung99]

@DaleStudy 리뷰해줘

[dalestudy]

Great job on submitting multiple solutions across different problems! Your code demonstrates solid understanding and implementation of dynamic programming, linked list manipulation, tree traversal, hash maps, and stack usage. Here are some suggestions to improve your code further:

1. Time & Space Complexity Comments:

   • Including brief complexity annotations (e.g., // TC: O(n), SC: O(1)) will help clarify your solutions' efficiency and assist future reviewers or debugging efforts.

2. Climbing Stairs (climbStairs):

   • Your DP approach is correct. To optimize space, consider using two variables instead of an array, reducing space complexity from O(n) to O(1).
   • Example: int prev = 1, curr = 1; then update iteratively.

3. Merge Two Sorted Lists:

   • Your current approach creates new nodes and assigns values, which can be simplified by using a dummy head node and directly manipulating pointers. This reduces the need for explicit value assignments and improves readability.
   • Also, consider handling edge cases at the start to avoid unnecessary null checks inside the loop.

4. Same Tree Check:

   • Using serialization with null markers is valid, but a recursive comparison of nodes could be more straightforward and efficient.
   • For example, a simple recursive method: compare current nodes, then recurse on left and right.

5. Two Sum:

   • Your approach of storing indices in a HashMap is good. To improve, you could handle the case where nums[i] * 2 == target more explicitly to avoid index errors or duplication.
   • Alternatively, a single-pass solution checking complement on the fly can be more concise.

6. Valid Parentheses:

   • Your stack-based method is clear and efficient. To enhance readability, consider using a HashMap to map closing to opening brackets, reducing multiple if statements.

Overall, your code is well-structured with clear logic. Fine-tuning with comments, optimizing space where possible, and simplifying some logic will make your solutions even more elegant. Keep up the great work—you're making excellent progress!

[jun-brro]

good code! merge-two-sorted-lists에서 tail pointer 옮겨가는 방식은 처음보는 접근이라 인상적입니다!

[chjung99]

good code! merge-two-sorted-lists에서 tail pointer 옮겨가는 방식은 처음보는 접근이라 인상적입니다!

리뷰 감사합니다!