Factorial

Input: 5

Output: 120

package jan27;

public class Factorial {
    public static void main(String[] args) {

        int n = 5;
        System.out.println(factorial(n));   // Output: 120 (5 * 4 * 3 * 2 * 1)
    }

    /**
     * Calculates factorial of n using recursion.
     *
     * Time Complexity: O(n)
     * - One recursive call per decrement from n to 0
     *
     * Space Complexity: O(n)
     * - Due to call stack depth in recursion from n down to 0
     */
    private static int factorial(int n) {
        if (n == 0) return 1;        // BASE CASE
        int temp = factorial(n - 1); // FAITH
        return n * temp;             // WORK
    }
}

📊 Summary Table:
Case
Time Complexity
Space Complexity
Explanation
All Cases
O(n)
O(n)
Recurses once per level; no loops or extra memory used