using namespace std;
// Some user defined magic constants used for hashing.

const int B = 31;
const int MOD = 666013;

const int P = 666013;
// Courtesy of Adrian Budau

struct myhash {
  size_t operator()(const vector<int>& v) const {
    size_t value = 1;
    for (auto x: v) {

      value = (value * B + hash<int>()(x)) % MOD;

      value = value * P + hash<int>()(x);

    }
    return value;
  }

vector<int> v = {1, 2, 3};
s.insert(v);
==

 
You don't need to worry about collisions, $unordered_set$ and $unordered_map$ will take care of that for you.