Recognizing & Mastering Coding?Patterns - Part 1: Two Pointer Technique (Opposite Ends)
Karrman Bhatia
R&D Engineer at Ansys | Ex - Siemens | TIET'23 | 3rd Rank in BTech @MIT ADT (ECE)
One thing becomes clear as we examine coding interviews in greater detail: it’s critical to recognize patterns. Understanding these crucial problem-solving patterns will help us identify common structures and use tried-and-true solutions instead of constantly starting from scratch. Among these is the Two Pointer Technique, which is both effective and powerful.
In this article, I’m kicking off the first installment of a series that explores different approaches to using the two-pointer method, starting with pointers at opposite ends.I’ll go over the fundamentals of this pattern, including what the method is, when and where to use it, and a carefully selected collection of LeetCode problems that are easy for beginners to understand. Stay tuned for more articles where I’ll dive into other essential strategies!
What is the Two-Pointer Technique?
The two-pointer technique is a problem-solving method that involves traversing an array or list with two pointers. Depending on the nature of the problem, these pointers may begin with:
This method is extremely effective when dealing with problems involving sorted arrays, subarrays, palindromes, or pair sums.
Two Pointers from Opposite?Ends
In problems where the array or string is sorted or involves comparison from both ends (e.g., checking for palindromes or reversing specific elements), it’s often useful to start the two pointers at opposite ends and move them towards each other. This allows you to narrow down the search space, making the solution much more efficient.
When to Use Two Pointers from Opposite?Ends?
There are some obvious clues in a problem description that suggest it might be best to use two pointers from opposite ends:
2. Pair, Triplet, or Subarray Problems:
3. Comparing Opposite Ends (Palindrome, Reverse):
4. Maximum or Minimum Difference Between Two Elements:
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Tips for Solving Problems with Two Pointers at Opposite?Ends
Example LeetCode?Problems
These EASY LeetCode problems, which heavily rely on the two-pointer technique with pointers starting at opposite ends, will help you get a grip of this method:
Why Pattern Recognition is Important
Understanding patterns like the two-pointer technique is essential for coding interviews and perfecting your problem-solving abilities. Instead of viewing each problem as an isolated incident, you’ll begin to recognize the underlying structure, allowing you to approach problems with confidence and efficiency.
In the next part of this series, I’ll go over how to use two pointers that start at the same end, which is a slightly different approach that solves a wide range of problems.
Conclusion
One of the most effective and adaptable coding techniques you have is the two-pointer technique. Today, we talked about how to use the technique with pointers at opposite ends and looked at some sample problems to get you started. I encourage you to test these on LeetCode to solidify your grasp of the pattern. In the next article, we’ll look at two pointers that start at the same end, opening up a whole new set of possibilities. Stay tuned for additional coding interview tips and patterns!
Request for?Action
You can’t master it without trying it! Put these patterns into practice right now. And I mean NOW!!
In the following section, we’ll look at even more strategies for solving problems involving two pointers. I’ll keep it concise to make it easy for you to revisit during revision. I’m also at a beginner-to-medium level, so feel free to reach out with any suggestions or tips. Don’t forget to share your experiences and let me know in the comments how these techniques have helped in your coding journey!
Thank you for sticking with me until the end! Keep pushing forward, and remember that practice makes perfect! ??
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