Tip 1: Practice at least 250 questions.
Tip 2: For example, complete at least 2 projects.
Tip 1: Include some real projects on your resume.
Tip 2: Avoid adding any false information to your resume.



All the integers in the array appear only once except for precisely one integer which appears two or more times.
You are given an integer array (ARR) of size N, which contains numbers ranging from 0 to (N - 2). Each number appears at least once. This means if N = 5, the array contains numbers from 0 to 3, and among these numbers, there is exactly one number that appears twice. Your task is to find and return the duplicate number present in the array.



You are given a 2D array of size Nx2, representing a set of 'N' intervals. Each interval consists of a starting point and an ending point. Your task is to find the maximum number of mutually disjoint intervals (intervals that do not overlap with each other).


The width of each bar is the same and is equal to 1.
Input: ‘n’ = 6, ‘arr’ = [3, 0, 0, 2, 0, 4].
Output: 10
Explanation: Refer to the image for better comprehension:

You don't need to print anything. It has already been taken care of. Just implement the given function.




You are given a linked list where each node contains two pointers. The first pointer points to the next node in the list, while the second pointer, called the random pointer, can point to any node in the list or be null. Your task is to create a deep copy of this linked list and return the head of the copied list. We will verify whether the copied linked list is an exact replica of the original list.

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What is recursion?