Decoding The Two Pointers Technique in DSA

When it comes to solving problems in Data Structures and Algorithms (DSA), one technique that stands out for its efficiency and versatility is the two-pointer technique. This technique is often used to solve array and linked list problems, and it shines in cases where you need to reduce time complexity and optimize your solution.

What is the Two Pointers Technique?

The two-pointer technique involves using two pointers that traverse the data structure (usually an array or a list) in a manner that helps you solve the problem more efficiently than iterating through it multiple times. The pointers are usually initialized at different positions within the structure, and depending on the problem, they can move towards each other or away from each other.

What I love about this technique is that it is fairly easy to learn. Let’s take the basic “String palindrome” problem.

Here’s a step by step on how to use 2 pointers to solve this problem-

1. Set Up Two Pointers:

   • Place one pointer at the start of the string (let's call it left) and another at the end of the string (let's call it right).

2. Compare Characters:

   • While the left pointer is less than the right pointer:

     • Check if the characters at these two pointers are the same.

     • If they are not the same, the string is not a palindrome, and you can return false.

     • If they are the same, move the left pointer one step to the right (increment) and the right pointer one step to the left (decrement).

3. Finish Checking:

   • If you finish comparing all character pairs without finding any mismatches, then return true, meaning the string is a palindrome.