cpp_unordered_map_helper.h

#include <functional>
#include <vector>

struct IntVectorHash {
  size_t operator()(const std::vector<int>& v) const {
    std::hash<int> hasher;
    size_t seed = 0;
    for (int i : v) {
      seed ^= hasher(i) + 0x9e3779b9 + (seed << 6) + (seed >> 2);
    }
    return seed;
  }
};