Addition of Recursion Problems in C++

[Upendra48]

I would like to add few basic recursion problems like:

1. Sum of the element of an array using recursion
2. Linear search using recursion
3. Find the peak in the mountain array using recursion
4. Find the pivot in a rotated sorted array using recursion
5. Factorial Calculation: A function to calculate the factorial of a number using recursion.
6. Fibonacci Sequence: A recursive function to find the nth Fibonacci number.
7. Binary Search: Implement a recursive binary search on a sorted array.
8. Power Calculation: Calculate a^b using recursion, covering both positive and negative powers.
9. Permutations of a String: Generate all permutations of a given string.
10. Tower of Hanoi: A classic recursion problem to move disks between rods.

(Please assign this issue to me and add hacktoberfest label)