Get permutation cycles.cpp

/*8<
  @Description:

    Receives a permutation [0, n-1] and return
    a vector 2D with each cycle.


>8*/
vll2d getPermutationCicles(const vll &ps) {
  ll n = len(ps);
  vector<char> visited(n);
  vector<vll> cicles;
  rep(i, 0, n) {
    if (visited[i]) continue;

    vll cicle;
    ll pos = i;
    while (!visited[pos]) {
      cicle.pb(pos);
      visited[pos] = true;
      pos = ps[pos];
    }

    cicles.push_back(vll(all(cicle)));
  }
  return cicles;
}