#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;
 
vector<int> interlace_vectors(const vector<int>& v1, const vector<int>& v2)
 {
      vector<int> result;
      for(size_t n = 0; n < max(v1.size(), v2.size()); ++n)
      {
           if(n < v1.size()) result.push_back(v1[n]);
           if(n < v2.size()) result.push_back(v2[n]);
      }
      return result;
 }
 
 int main()
 {
     vector<int> v1 = {4,7,9,3,1};
     vector<int> v2 = {3,6,9};
     vector<int> v3 = interlace_vectors(v1, v2);
 
     // for(int n: v3)
     //     cout << n << ' ';
     // LWS is down at the moment, IDEone has an old compiler, so another way to loop:
     for_each(v3.begin(), v3.end(), [](int n){cout << n << ' ';});
     cout << '\n';
 
 }

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