#include <utility>
#include <vector>
#include <iterator>
 
template <typename It>
std::vector<std::pair<It,It>> chunk(It first, It last, unsigned bucket_size)
{
  std::vector<std::pair<It,It>> ret;
  unsigned count=std::distance(first, last);
  ret.reserve(count/bucket_size+1);
  for( ; count >= bucket_size; count -= bucket_size) {
    It endchunk = std::next(first, bucket_size);
    ret.push_back(std::make_pair(first, endchunk));
    first = endchunk;
  }
  if (first!= last)
    ret.push_back(std::make_pair(first, last));
  return ret;
}
 
int main() {
  std::vector<int> input(100);
  auto res = chunk(input.begin(), input.end(), 9);
}

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