Navie 并查集解法！

#include <iostream>
#include <vector>

using namespace std;
int t, n, m, u, v;

int Find(vector<int>& p, int x) {
  return p[x] == -1 ? x : p[x] = Find(p, p[x]);
}

void Union(vector<int>& p, int u, int v, int& k) {
  if (Find(p, u) == Find(p, v)) return;
  p[Find(p, u)] = Find(p, v);
  ++k;
}

int main(void) {
  scanf("%d", &t);
  for (int i = 1; i <= t; ++i) {
    scanf("%d %d", &n, &m);

    vector<int> p(n + 1, -1);
    int k = 0;
    while (m--) {
     scanf("%d %d", &u, &v);
     Union(p, u, v, k);
    }

    printf("Case #%d: %d\n", i, k  + ((n - 1 - k) << 1));
  }
}