1987 - 小丑竟在我身边

77475

bjtu/1987/1987.cpp

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+#include <iostream>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 1e4 + 5;
+
+int n, m, cnt, cnt2;
+std::vector<int> g[N];
+bool vis[N], flag = true;
+
+void dfs(int u) {
+    cnt++;
+    vis[u] = true;
+
+    for (int v : g[u]) {
+        if (!vis[v]) dfs(v);
+    }
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n >> m;
+
+    for (int i = 1, u, v; i <= m; i++) {
+        cin >> u >> v;
+
+        g[u].emplace_back(v);
+        g[v].emplace_back(u);
+    }
+
+    for (int i = 1; i <= n; i++) {
+        if (!vis[i]) {
+            int pre = cnt;
+            dfs(i);
+
+            if (cnt - pre > 1) cnt2++;
+        }
+    }
+
+    cout << (cnt2 <= 1 ? "YES" : "NO") << endl;
+
+    return 0;
+}