feat: Add PrintNumbersBackward class with recursive countdown

WHAT the code does:
- Defines a `PrintNumbersBackward` class that prints numbers in reverse using recursion.
- `countBackwards(int n)`:
  - **Base case**: if `n == 0`, prints `"Done!"`.
  - **Recursive case**: prints current `n`, decrements it, and calls `countBackwards(n)` again.
- `main()` calls `countBackwards(7)` to start the countdown.

WHY this matters:
- Demonstrates **recursion with a decreasing counter**.
- Shows how to build both a **base case** (termination) and **recursive case** (progress).
- Useful for teaching recursion flow and call stack behavior.

HOW it works:
1. `countBackwards(7)` prints `7` → calls `countBackwards(6)`.
2. Prints numbers down to `1`.
3. At `n == 0`, prints `"Done!"` and recursion terminates.

Tips & gotchas:
- Works only for non-negative numbers; negative input would recurse infinitely.
- Tail recursion optimization is not supported in Java → large `n` may cause `StackOverflowError`.
- Could be rewritten iteratively for efficiency in production, but recursion is clearer for learning.

Use-cases:
- Educational example for recursion basics.
- Can be adapted for countdown timers, loops expressed recursively, or reverse iteration problems.
- Useful in interviews to demonstrate recursive thinking.

Short key: algo-recursive-countdown.

Signed-off-by: https://github.com/Someshdiwan <[email protected]>

Author: Someshdiwan

Section10Methods/RecurssionPractice/src/PrintNumbersBackward.java

@@ -3,11 +3,10 @@ public static void main(String[] args) {
         countBackwards(7);
     }
     public static void countBackwards(int n){
-        if(n==0)
-        {
+        if(n==0) {
             System.out.println("Done!");
         }
-        else{
+        else {
             System.out.println(n);
             n--;
             countBackwards(n);