题解 | 连通图

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <vector>
using namespace std;
int father[1000];
void InitT(int n) {
    for (int i = 0; i < n; ++i) {
        father[i] = i;
    }
}
int FindT(int u) {
    if (u == father[u]) { return u; }
    else {
        father[u] = FindT(father[u]);
        return father[u];
    }
}
void UnionT(int u, int v) {
    int uroot = FindT(u);
    int vroot = FindT(v);
    father[vroot] = uroot;
}
int main() {
    int n, m, x, y;
    while (scanf("%d%d", &n, &m) != EOF) {
        if (n == 0 && m == 0) { break; }
        vector<int> rootnum;
        InitT(n+1);
        for (int j = 0; j < m; ++j) {
            scanf("%d%d", &x, &y);
            UnionT(x, y);
        }
        for (int k = 1; k <= n; ++k) {
            if (k==father[k]) { rootnum.push_back(k); }
        }
        if (rootnum.size() >= 2) { printf("NO\n"); }
        else { printf("YES\n"); }
    }
}