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