new file: B2169.cpp

B2169.cpp

@@ -0,0 +1,34 @@
+#include <bits/stdc++.h>
+using namespace std;
+int n;
+vector<int> fri[500005];
+bool vis[500005];
+vector<int> cc;
+void dfs(int now)
+{
+    vis[now] = 1;
+    cc.push_back(now);
+    for (auto k : fri[now])
+    {
+        if (!vis[k])
+            dfs(k);
+    }
+}
+int main()
+{
+    scanf("%d", &n);
+    for (int i = 1, u, v; i < n; ++i)
+    {
+        scanf("%d%d", &u, &v);
+        fri[u].push_back(v);
+        fri[v].push_back(u);
+    }
+    for (int i = 1; i <= n; ++i)
+    {
+        sort(fri[i].begin(), fri[i].end());
+    }
+    dfs(1);
+    for (auto k : cc)
+        printf("%d ", k);
+    return 0;
+}