Disjoint Set Algorithm !

#include <iostream>
#include <vector>
#include <unordered_map>
#include <numeric>

using namespace std;
int n, m;

class DSU {
public:
  DSU(int n) : count_(n), p_(n + 1) {
    iota(begin(p_), end(p_), 0);
  }
  ~DSU() {}

  int Find(int x) {
    return p_[x] ^ x ? p_[x] = Find(p_[x]) : x;
  }

  void Union(const int u, const int v) {
    const int pu = Find(u);
    const int pv = Find(v);
    if (pu == pv) return;
    p_[pu] = pv;
    --count_;
  }

  int get_count() const {
    return count_;
  }

private:
  int count_;
  vector<int> p_;
};


int main(void) {
  scanf("%d", &n);
  scanf("%d", &m);

  DSU dsu(n);
  unordered_map<int, vector<int>> mp;

  while (m--) {
    char op;
    int a, b;
    cin >> op >> a >> b;
    switch (op) {
      case 'F': dsu.Union(a, b); break;
      case 'E': mp[a].emplace_back(b), mp[b].emplace_back(a); break;
    }
  }

  //  我敌人的敌人也是我的朋友。
  for (auto&& [k, v] : mp)
    for (int i = 1; i < v.size(); ++i)
      dsu.Union(v[0], v[i]);

  // for (auto&& [k, v] : mp)
  //   for (int i = 0; i < v.size() - 1; ++i)
  //     dsu.Union(v[i], v[i + 1]);

  printf("%d\n", dsu.get_count());
}