Easy Level

1. Write a program to reverse an array or string
2. A Boolean Matrix Question
3. Count frequencies of all elements in array in O(1) extra space and O(n) time
4. Find common elements in three sorted arrays
5. Program for Armstrong Numbers
6. Run Length Encoding
7. Sieve of Eratosthenes
8. Find the middle of a given linked list in C and Java
9. Write a Program to Find the Maximum Depth or Height of a Tree
10. Write an Efficient Function to Convert a Binary Tree into its Mirror Tree
11. Diameter of a Binary Tree
12. Maximum width of a binary tree
13. Sorted Array to Balanced BST
14. Stack | Set 2 (Infix to Postfix)

Medium Level

1. A program to check if a binary tree is BST or not
2. Detect and Remove Loop in a Linked List
3. Dynamic Programming | Set 11 (Egg Dropping Puzzle)
4. Find a pair with given sum in a Balanced BST
5. Reverse a Linked List in groups of given size

Hard Level

1. Given an array arr[], find the maximum j – i such that arr[j] > arr[i]