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OI-codes/AtCoder/ABC231/D/D.cpp

47 lines
851 B
C++

#include <cstdio>
#include <cstdlib>
#include <vector>
int n, m, a, b;
bool vis1[100005], vis2[100005];
std::vector<int> g[100005];
void dfs(int u, int f) {
vis1[u] = 1;
if (vis2[u]) {
printf("No\n");
exit(0);
}
vis2[u] = true;
for (int v : g[u]) {
if (v == f) continue;
dfs(v, u);
}
vis2[u] = false;
}
int main() {
scanf("%d%d", &n, &m);
if (m >= n) {
printf("No\n");
exit(0);
}
for (int i = 1; i <= m; i++) {
scanf("%d%d", &a, &b);
g[a].push_back(b);
g[b].push_back(a);
}
for (int i = 1; i <= n; i++) {
if (!vis1[i])
dfs(i, i);
}
for (int i = 1; i <= n; i++) {
if (g[i].size() > 2) {
printf("No\n");
exit(0);
}
}
printf("Yes\n");
return 0;
}