merge 2-d arrays(store them as 1-d vector, because it's easy to serialize)

vector-merge.cc

#include <iostream>
#include <vector>

using namespace std;

#define IndexType int

void merge_local_vectors(vector<IndexType> &first, vector<IndexType> &second, int pair_size1, int pair_size2, int key1, int key2) {
    int ssz1 = first.size(), ssz2 = second.size();
    int i = 0, j = 0;

    vector<IndexType> res;
    res.reserve(ssz1 + ssz2);
    cout << res.size() << endl;

    auto it1 = first.begin(), it2 = second.begin();
    while (i < ssz1 && j < ssz2) {
        if (first[i + key1] <= second[j + key2]) {
            res.insert(res.end(), it1 + i, it1 + i + pair_size1);
            i += pair_size1;
        } else {
            res.insert(res.end(), it2 + j, it2 + j + pair_size2);
            j += pair_size2;
        }

        cout << "size of res : " << res.size() << endl;
    }

    while (i < ssz1) {
        res.insert(res.end(), it1 + i, it1 + i + pair_size1);
        i += pair_size1;
    }

    while (j < ssz2) {
        res.insert(res.end(), it2 + j, it2 + j + pair_size2);
        j += pair_size2;
    }

    first.assign(res.begin(), res.end());
}

int main(int argc, char *argv[]) {
    vector<IndexType> first = {12, 5, 14, 8, 16, 12, 24, 5, 30, 5};
    vector<IndexType> second = {14, 5, 18, 10, 28, 12};

    merge_local_vectors(first, second, 2, 2, 0, 0);

    cout << "size of first : " << first.size() << endl;
    for (auto vi : first) {
        cout << vi << " ";
    }
    cout << endl;
}

/*

output : 

0
size of res : 2
size of res : 4
size of res : 6
size of res : 8
size of res : 10
size of res : 12
size of res : 14
size of first : 16
12 5 14 8 14 5 16 12 18 10 24 5 28 12 30 5

*/