Questions

9 of 19

1What is the Prefix Sum technique?

2Why is insertion/deletion in the middle of an array O(n)?

3Explain the concept of Amortized O(1) for Dynamic Array insertion.

4How do you find the second largest element in an unsorted array?

5What is the difference between a String and a Character Array?

6What is the Sliding Window technique? Give a use case.

7What is a Sparse Array? When is it useful?

8Why is string concatenation in a loop O(n²)? How do you fix it? (StringBuilder)

9What is the Two-Pointer technique? Give a use case.

10What is a Dynamic Array (ArrayList/Vector)? How does it grow?

11What are the advantages and disadvantages of Arrays?

12What is an Array? How is it stored in memory?

13Explain Kadane's Algorithm (Maximum Subarray Sum). What is its complexity?

14Why are Strings immutable in Java/C#? What are the benefits?

15What is String Interning?

16Explain how to find the longest palindromic substring.

17Why is accessing an array element O(1)?

18How do you check if two strings are anagrams of each other?

19How do you rotate an array by k positions? (In-place vs extra space)

Data-Structures

Data-Structures

Complexity Analysis

Arrays and Strings

Stacks and Queues

09 / 19

What is the Two-Pointer technique? Give a use case.

Difficulty: 3/10

Two-Pointer Technique

The Two-Pointer technique uses two indexes that move through a data structure according to the problem's constraints. It is especially effective for sorted arrays, partitioning problems, and string comparisons.

javascript

1
A classic use case is Two Sum in a sorted array.
2
The technique can reduce an O(n²) brute-force search to O(n).
3
It is also useful for palindrome validation and array partitioning.
4
Correct pointer movement depends on an invariant, such as sorted order.

Follow-up Questions

How is Two-Pointer different from Sliding Window?
Can Two-Pointer solve Three Sum?

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