AoC day 16 part 2

#include <iostream>
#include <sstream>
#include <vector>
#include <numeric>
#include <algorithm>
#include <functional>

using namespace std::placeholders;

void shift(std::vector<char>& dance, int val) {
  for (int i = 0; i < val; i++) {
    char c = dance.back(); dance.pop_back();
    dance.insert(dance.begin(), c);
  }
}

void exchange(std::vector<char>& dance, int a, int b) {
  int tmp = dance[a];
  dance[a] = dance[b];
  dance[b] = tmp;
}

void partner(std::vector<char>& dance, char c1, char c2) {
  auto p1 = std::find(std::begin(dance), std::end(dance), c1);
  auto p2 = std::find(std::begin(dance), std::end(dance), c2);
  std::iter_swap(p1, p2);
}

void print(std::vector<char>& dance) {
  for (auto& c: dance)
    std::cout << c;
  std::cout << std::endl;
}

int main() {
  std::string input, token;
  std::getline(std::cin, input);
  std::stringstream ss(input);

  std::vector<char> dance(16);
  std::iota(dance.begin(), dance.end(), 'a');

  std::vector<std::function<void(std::vector<char>&)>> call;

  while (std::getline(ss, token, ',')) {
    if (token.empty()) continue;
    switch (token[0]) {
      case 's': {
        int s = std::stoi(token.substr(1))%16;
        auto x = std::bind(shift, _1, s);
        call.push_back(x);
      } break;
      case 'x': {
        auto pos = token.find('/');
        int a = std::stoi(token.substr(1, token.size()-pos));
        int b = std::stoi(token.substr(pos+1));
        auto x = std::bind(exchange, _1, a, b);
        call.push_back(x);
      } break;
      case 'p': {
        auto x = std::bind(partner, _1, token[1], token[3]);
        call.push_back(x);
      } break;
      default: break;
    }
  }

  // find cycle
  auto copy = dance;
  unsigned long long cycle = 0;
  do {
    for (auto& c: call)
      c(copy);
    cycle++;
  } while (copy != dance);

  std::cout << "Cycle: " << cycle << std::endl;

  for (unsigned long long i = 0; i < 1000000000 % cycle; i++) {
    for (auto& c: call)
      c(dance);
  }

  print(dance);

  return 0;
}