1. Two number sum
   [3, 5, -4, 8, 11, 1, -1, 6], 10
   Task: check if there are two numbers in an array which sum equals to required, i.e. 11 + (-1) = 10

2. Validate subsequence
   [5, 1, 22, 25, 6, -1, 8, 10], [1, 6, -1, 10]
   Task: check if the second array is a valid subsequence of the first one

3. Find the closest value in binary search tree
   Task: find the closest value to the target value that contain in the bst

4. Branch sums
   Task: find sums of all branches in binary tree

5. Node depth
   Task: find sum of all nodes depths

6. Three numbers sum
   Task: find all possible three numbers combinations which sum is equal to required

7. Subbaray sort
   Task: find minimum sub array when sorted is going make entire array sorted

8. Binary search tree construction
   Task: construct BST with following methods:

• insertion
• searching
• deletion

9. Validate binary search tree
   Task: validate BST

10. Quick sort
    Task: implement quick sort algorithm

11. Spiral Traverse
    Task: write a function that returns a 1-dimensional array from 2-dimensional array in spiral order

12. BST Traversal
    Task: traverse BST

13. Merge Sort
    Task: sort array using merge sort

14. Heap Sort
    Task: sort array using heap sort

15. Move element to end
    Task: move element(s) to the end of an array

16. Invert binary tree
    Task: invert a provided binary tree