Merge Sorted Array

Merge two arrays that are each sorted in non-decreasing order into one sorted array.

Input:

• line 1: m n — the sizes of the two arrays
• line 2: the m values of the first array (empty if m = 0)
• line 3: the n values of the second array (empty, or missing, if n = 0)

Output: all m + n values in sorted order on one line.

Constraints: 0 ≤ m, n ≤ 10⁵, 1 ≤ m + n, −10⁹ ≤ value ≤ 10⁹.

Tip: reading all numbers as whitespace-separated tokens (instead of line by line) handles the empty lines for free.

Challenge: the classic version merges in place into the first array (which has room for both). The trick: fill it from the back, comparing the largest remaining values. Here, aim for O(m + n) — don't just concatenate and sort.