feat: Add PrimeOrNot class with isPrime method for prime number check

WHAT the code does:
- Defines a `PrimeOrNot` class with a static method `isPrime(int x)`.
- `isPrime()` checks if a number is prime:
  - Returns `false` for numbers ≤ 1.
  - Loops from `2` to `x/2` checking divisibility.
  - Returns `false` if any divisor is found, otherwise `true`.
- `main()` tests the method with numbers: 13, 91, 100, 2, and 1.

WHY this matters:
- Demonstrates prime number validation using basic loops and conditions.
- Reinforces modular arithmetic (`%`) and control flow.
- A classic programming exercise useful in interviews and algorithm practice.

HOW it works:
1. Input `x = 13` → loop finds no divisor → returns `true`.
2. Input `x = 91` → divisible by 7 → returns `false`.
3. Input `x = 100` → divisible by 2 → returns `false`.
4. Input `x = 2` → no divisors found → returns `true`.
5. Input `x = 1` → `<= 1` check → returns `false`.

Tips & gotchas:
- The loop `i <= x/2` works but is inefficient for large numbers → can be optimized to `i <= Math.sqrt(x)`.
- Handles negative numbers by treating them as not prime.
- For efficiency, you could check divisibility by 2 first, then loop odd numbers only.
- Returning early on divisor detection keeps it performant.

Use-cases:
- Educational example for prime checking.
- Useful in math-heavy applications or competitive programming.
- Can serve as a utility function in algorithms needing prime detection.
- Good base for extending to prime factorization.

Short key: algo-prime-check-basic.

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

Author: Someshdiwan

Section10Methods/Methods 2.O/src/PrimeOrNot.java

@@ -1,22 +1,37 @@
 public class PrimeOrNot {
-    public static void main(String[] args)
-    {
+    public static void main(String[] args) {
         System.out.println(isPrime(13));
         System.out.println(isPrime(91));
         System.out.println(isPrime(100));
+        System.out.println(isPrime(2));
+        System.out.println(isPrime(1));
     }
 
-    public static boolean isPrime(int x)
-    {
-        //13 --> 1,2,3,4,5,6,7,8,9,10,11,12,13
-        int res = 0;
-        for (int i = 1; i < x / 2; i++)
+    /*
+    Declaring a method 'isPrime'. and call this method into thr main method.
+
+    A prime number is a number greater than 1 that has exactly two factors: 1 & itself.
+    Examples:
+    2 → factors: 1, 2 → prime ✅
+    3 → factors: 1, 3 → prime ✅
+    4 → factors: 1, 2, 4 → not prime ❌(extra factor)
+    13 → factors: 1, 13 → prime ✅
+    */
+
+    public static boolean isPrime(int x) {
+        if (x <= 1) return false; // 0 and 1 are not prime.
+
+        for (int i = 2; i <= x / 2; i++)
         {
-            if (x % i == 0)
-            {
-                res++;
+            if (x % i == 0) {
+                return false; // found a divisor → not prime.
             }
         }
-        return res == 1;
+        return true; // no divisors found → prime
     }
-}
+}
+
+/*
+i <= x / 2; → keep looping until half of the number.
+Why? Because a number can’t have a factor greater than x/2 (except itself).
+*/