DAY 18 Solving Complex Two-Pointer Problems

Hello Everyone!

I’m Somuya Khandelwal, back with updates from Day 3 of Week 4 in my competitive programming journey. Today, I focused on Two-Pointer Problems, a highly efficient approach for solving array and string-related challenges. These problems required me to think critically about optimization and edge case handling, all while writing clean, structured code.

What I Worked On Today

1. Text Justification (Hard Difficulty)

   • Task: Format an array of words into fully justified lines, each fitting within a given max width.
   • Approach:
     • Used two pointers to group words that fit within the max width.
     • Carefully distributed spaces between words and handled special cases like single-word lines or the last line.
   • What I Learned:
     • Formatting problems require breaking the task into manageable steps—grouping words, balancing spaces, and handling edge cases.
     • Special cases like the last line and single-word formatting need extra attention for accuracy.

2. Container With Most Water (Medium Difficulty)

   • Task: Find two lines in an array that form a container with the maximum amount of water.
   • Approach:
     • Used a two-pointer technique, starting with pointers at the beginning and end of the array.
     • Moved the pointer corresponding to the smaller height inward to maximize the area.
   • What I Learned:
     • The two-pointer method is ideal for problems that involve minimizing or maximizing values in a sorted or semi-sorted structure.
     • Simplifying the logic by focusing on the limiting factor (smaller height in this case) leads to an efficient solution.

3. 3 Sum (Medium Difficulty)

   • Task: Find all unique triplets in an array that sum to zero.
   • Approach:
     • Sorted the array and used a fixed number as the first element, applying the two-pointer technique to find pairs that sum to the negative of the fixed number.
     • Skipped duplicates to avoid redundant triplets.
   • What I Learned:
     • Combining sorting with the two-pointer technique reduces the complexity of multi-condition problems.
     • Efficiently managing duplicates ensures both correctness and performance.

What I Learned Today

1. The Versatility of Two Pointers:

   • Problems like Container With Most Water and 3 Sum showed how the two-pointer technique simplifies optimization tasks.

2. Breaking Down Complex Formatting Tasks:

   • In Text Justification, dividing the task into smaller steps—word grouping, space distribution, and edge case handling—helped tackle the problem effectively.

3. Sorting Before Two Pointers:

   • Sorting arrays before applying the two-pointer method streamlines logic, especially for problems like 3 Sum, where duplicates can complicate the solution.

4. Debugging Multi-Condition Problems:

   • Challenges like Text Justification required careful debugging to ensure all scenarios—such as uneven spacing or last-line formatting—were handled correctly.

Reflections and Challenges

The Text Justification problem stood out as the most challenging today. Balancing the space distribution while ensuring the final line met the requirements took a lot of trial and error, but solving it was extremely satisfying. 3 Sum reinforced the importance of managing duplicates efficiently, which required attention to detail in both the sorting and two-pointer logic.

Overall, these problems helped me appreciate the power of the two-pointer technique and how it can simplify complex tasks when used effectively.

Looking Ahead

Tomorrow, I’ll dive into Sliding Window Problems, tackling challenges like Substring With Concatenation of All Words and Minimum Window Substring. These problems will test my ability to dynamically manage windows while solving substring-related tasks.

Thank you for following along on my journey! I’m excited to continue learning and growing as I explore more exciting challenges in competitive programming.

Best regards,

Somuya