Print Increasing Decreasing

Input: 5
Output: 1 2 3 4 5 5 4 3 2 1 

package jan27;

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

        int n = 5;
        increasingDecreasing(1, n); // EXPECTATION: 1 2 3 4 5 5 4 3 2 1
    }

    /**
     * Prints numbers in increasing and then decreasing order using recursion.
     *
     * Time Complexity: O(n)
     * - Each number from 1 to n is printed twice (before and after recursion).
     * - But overall complexity is still O(n) since print is O(1).
     *
     * Space Complexity: O(n)
     * - Due to recursive call stack that grows from 1 to n.
     */
    private static void increasingDecreasing(int val, int n) {
        if (val > n) return;          // BASE CASE
        System.out.println(val);     // WORK (increasing part)
        increasingDecreasing(val + 1, n);   // FAITH
        System.out.println(val);     // WORK (decreasing part)
    }
}

Expectataion of f(1,n) => FAITH f(2, n) it will print 2 3 4 5 5 4 3 2

Then before and after f(2, n) we'll print '1' as WORK

📊 Summary Table:

Case
Time Complexity
Space Complexity
Explanation
All Cases
O(n)
O(n)
One recursive call per lev