random sets

#include <vector>
#include <cstdlib>
#include <ctime>
#include <algorithm>
#include <iostream>

/*
 * Generates 11 sets of 6 random numbers [0..50) without copies
 */
int main()
{
  // seed random number generator
  std::srand(std::time(NULL));

  std::vector<int> src;
  std::vector< std::vector<int> > ret;
  for (int j = 1; j <= 49; ++j)
    src.push_back(j);
  for (size_t i = 0; i < 11; ++i) {

    // insert new vector in back
    ret.push_back(std::vector<int>());
    // work with reference to new vector, avoids later copy
    std::vector<int>& out = ret.back();

    // remaining numbers to pick from
    size_t range = src.size();
    for (size_t j = 0; j < 6; ++j) {
      // pick a value
      size_t index = std::rand() % range;
      out.push_back(src[index]);

      /* take the picked number out of range by swapping it with the last
       * value, then shrinking range
       */
      std::swap(src[index], src[range - 1]);
      range -= 1;
    }
    std::sort(out.begin(), out.end());
  }

  for (size_t i = 0; i < ret.size(); ++i) {
    for (size_t j = 0; j < ret[i].size(); ++j) {
      std::cout << ret[i][j] << " ";
    }
    std::cout << std::endl << std::endl;
  }

  return 0;
}