模板题，答案需要-1，三个村只需要两条路

cpp
#include <iostream>
#include <vector>
using namespace std;

const int maxn = 1000;

int father[maxn];

int find(int x) {
    if (father[x] != x) {
        father[x] = find(father[x]);
    }
    return father[x];
}

void unionn(int x, int y) {
    int root_x = find(x);
    int root_y = find(y);
    if (root_x != root_y) {
        father[root_x] = root_y;
    }
}

int main() {
    int n, m;
    while (cin >> n >> m && n != 0) {
        for (int i = 1; i <= n; ++i) {
            father[i] = i;
        }

        for (int i = 0; i < m; ++i) {
            int a, b;
            cin >> a >> b;
            unionn(a, b);
        }

        // Count the number of unique sets
        int unique_sets = 0;
        for (int i = 1; i <= n; ++i) {
            if (father[i] == i) {
                unique_sets++;
            }
        }

        // Calculate the number of roads needed to connect all sets
        int roads_needed = unique_sets - 1;

        cout << roads_needed << endl;
    }

    return 0;
}