Array Sum

• Time : $O(n)$
• Space : $O(n)$

vector<int> Solution::addArrays(vector<int> &A, vector<int> &B) {
    reverse(begin(A), end(A));
    reverse(begin(B), end(B));
    int p = 0, carry = 0;
    vector<int> res;
    while(p < A.size() and p < B.size()) {
        int now = carry + A[p] + B[p];
        res.push_back(now % 10);
        carry = now / 10;
        p += 1;
    }
    while(p < A.size()) {
        int now = carry + A[p];
        res.push_back(now % 10);
        carry = now / 10;
        p += 1;
    }
    while(p < B.size()) {
        int now = carry + B[p];
        res.push_back(now % 10);
        carry = now / 10;
        p += 1;
    }
    
    reverse(begin(res), end(res));
    return res;
}