Lintcode: Merge Sorted Array II

Merge two given sorted integer array A and B into a new sorted integer array.

Example
A=[1,2,3,4]

B=[2,4,5,6]

return [1,2,2,3,4,4,5,6]

Challenge
How can you optimize your algorithm if one array is very large and the other is very small?

class Solution {
/**
* @param A and B: sorted integer array A and B.
* @return: A new sorted integer array
*/
public ArrayList<Integer> mergeSortedArray(ArrayList<Integer> A, ArrayList<Integer> B) {
// write your code here
if (A==null || A.size()==0) return B;
if (B==null || B.size()==0) return A;
ArrayList<Integer> res = new ArrayList<Integer>();
int i=0, j=0;
for (int k=0; k<A.size()+B.size(); k++) {
if (i<A.size() && j<B.size() && A.get(i) < B.get(j)) {
res.add(A.get(i));
i++;
}
else if (i<A.size() && j<B.size() && A.get(i) >= B.get(j)){
res.add(B.get(j));
j++;
}
else if (i<A.size()) {
res.add(A.get(i));
i++;
}
else {
res.add(B.get(j));
j++;
}
}
return res;
}
}