Recursive Searching and Sorting (Binary Search, Merge Sort)

AP Computer Science A· difficulty 4/5

public static void sort(int[] a, int lo, int hi) {
    if (lo >= hi) return;
    int mid = (lo + hi) / 2;
    sort(a, lo, mid);
    sort(a, mid + 1, hi);
    // merge halves...
}

Which is the correct base case for this mergesort skeleton?

A
$lo >= hi (single element or empty)$
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B
$lo == 0$
C
$hi == a.length$
D
$lo + hi == 0$

Explanation

A single (or empty) range is already sorted, so recursion stops when lo >= hi.

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