#include <vector>
#include <list>
#include <iostream>
#include <iomanip>

using namespace std;

template<typename T>
void print(vector<T> v) {
  for(auto it = v.cbegin(); it!=v.cend(); it++) 
    cout << setw(3) << *it;
  cout << endl;
}

int main() {
  vector<int> ints;                  // initially zero size
  for(int i=0; i<10; i++) {
    ints.push_back(i+1);             // insert to the end - very fast
    ints.insert(ints.begin(),i+1);   // insert to the beginning - extremely slow
  }
  print(ints);
  
  while(ints.size() > 0) {
    ints.erase(ints.begin());    // erase the first element.
    ints.erase(ints.end()-1);    // erase the laste element.
    print(ints);
  }
}