Print Decreasing Increasing

Input: 5

Output: 5 4 3 2 1 1 2 3 4 5

package jan27;

public class DecreasingIncreasing {
    public static void main(String[] args) {
        int n = 5;
        decreasingIncreasing(n);    // Output: 5 4 3 2 1 1 2 3 4 5
    }

    /**
     * Prints numbers in decreasing then increasing order using recursion.
     *
     * Time Complexity: O(n)
     * - One recursive call for each n down to 1, and two print operations per level.
     * - But still linear because print is constant time.
     *
     * Space Complexity: O(n)
     * - Due to recursive call stack growing to depth n before unwinding.
     */
    private static void decreasingIncreasing(int n) {
        if (n == 0) // BASE CASE
            return;

        System.out.println(n);            // WORK (before recursive call)
        decreasingIncreasing(n - 1);      // FAITH
        System.out.println(n);            // WORK (after recursive call)
    }
}

Expectation is f(5) => f(4) will print 4 3 2 1 1 2 3 4

Then Work is sout(5) before and after f(4).

Case
Time Complexity
Space Complexity
Explanation
All Cases
O(n)
O(n)
One recursive call per level; prints twice per call but stack grows to n