#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <cassert>
 
std::vector<int> convert(const std::string& s)
{
  std::vector<int> r;
  std::transform(s.begin(), s.end(), std::back_inserter(r), [](auto e) {return e - '0'; });
  return r;
}
 
std::string convert(const std::vector<int>& v)
{
  std::string r;
  std::transform(v.begin(), v.end(), std::back_inserter(r), [](auto e) {return e + '0'; });
  return r;
}
 
std::vector<int> convert(const int n)
{
  return convert(std::to_string(n));
}
 
 
int main()
{
  auto v = convert(3215);
  auto s = convert(v);
  assert(s == "3215");
}

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