假入门？没关系13行秒了

#include <iostream>
#include <cstdio>
using namespace std;
int a[1005], b[1005], c[2005];
int n, m, i = 1, j = 1, k = 1;
int main(){
	cin >> n >> m;
	for(int i = 1; i <= n + m; i++) cin >> (i <= n ? a[i] : b[i - n]);
	while(i <= n && j <= m) c[k++] = (a[i] < b[j] ? a[i++] : b[j++]);
	while(i <= n) c[k++] = a[i++]; while(j <= m) c[k++] = b[j++];
	for(int i = 1; i <= n + m; i++) cout << c[i] << ' ';
	return 0;
}

甚至 $O(n+m)$