题解 | 畅通工程

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <vector>
using namespace std;
int father[1000];
void Initit(int n) {
    for (int i = 1; i <=n; ++i) {
        father[i] = i;
    }
}
int Findit(int u) {
    if (u==father[u]) { return u; }
    else {
        father[u] = Findit(father[u]);
        return father[u];
    }
}
void Unionit(int u, int v) {
    int uroot = Findit(u);
    int vroot = Findit(v);
    father[vroot] = uroot;
}
int main() {
    int n, m;
    while (scanf("%d%d", &n, &m) != EOF) {
        if(n==0){break;}
        vector<int> link;
        Initit(n);
        int fu, zi;
        for (int i = 0; i < m; ++i) {
            scanf("%d %d", &fu, &zi);
            Unionit(fu, zi);
        }
        for (int j = 1; j <= n; ++j) {
            if (father[j] == j) { link.push_back(j); }
        }
        if (link.size() == 1) { printf("0\n"); }
        else { printf("%d\n", link.size() - 1); }
    }
}