cxx17/cx_shuffle.cc

// An iterator that shuffles over a vector.

#define CATCH_CONFIG_MAIN
#include <catch.hpp>

#include <experimental/string_view>
#include <sstream>
#include <vector>
#include <range/v3/all.hpp>
#include <cstdlib>

using string_view = std::experimental::string_view;

// Should work over any SequenceContainer.
template <typename Container>
std::string join(const Container& vect, string_view sep = " ") {
  auto i = 0;
  std::stringstream out;

  for (const auto& item : vect) {
    if (i != 0) {
      out << sep;
    }
    out << item;
    i++;
  }

  return out.str();
}

template <typename Container>
Container shuffle_1(const Container& src) {
  using pair = std::pair<size_t, int>;
  std::vector<pair> indexes;
  int i = 0;

  for (size_t i = 0; i < src.size(); i++) {
    indexes.emplace_back(pair{i, std::rand()});
  }
  std::cout << join(indexes | ranges::view::keys) << "\n";

  std::sort(indexes.begin(), indexes.end(), [](auto lhs, auto rhs) { return lhs.second < rhs.second; });

  Container out;
  for (auto key : indexes | ranges::view::keys) {
    out.emplace_back(src[key]);
  }

  return out;
}

template <typename Container>
Container shuffle(const Container& src) {
  Container dup{src};

  for (size_t i = 0; i < src.size(); i++) {
    std::swap(dup[i], dup[std::rand() % src.size()]);
  }

  return dup;
}

TEST_CASE("cx_shuffle", "shuffle") {
  std::vector<int> items{1, 2, 3, 4, 5, 6};

  CHECK(join(items) == "1 2 3 4 5 6");
  CHECK(join(shuffle(items)) == "2 1 4 5 6 3");
}