10 Tail-recursive accumulator sums 4+3+2+1 = 10.

Recursion

AP Computer Science A· difficulty 3/5

public static int sum(int n) { return helper(n, 0); }
private static int helper(int n, int acc) {
    if (n == 0) return acc;
    return helper(n - 1, acc + n);
}
System.out.println(sum(4));

What is printed?

A
$10$
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B
$4$
C
$0$
D
$24$

Explanation

Tail-recursive accumulator sums 4+3+2+1 = 10.

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