P1395 会议

https://www.luogu.com.cn/record/169660795

Luogu/P1395/P1395.cpp

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+#include <iostream>
+#include <numeric>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 5e4 + 5;
+
+int n;
+int siz[N],     // siz: 子树大小（所有子树上节点数 + 该节点）
+    weight[N];  // weight: 所有子树大小最大值
+int centroid;   // centroid: 重心
+int dep[N];
+std::vector<int> g[N];
+
+void dfs1(int u, int f) {
+    siz[u] = 1;
+    weight[u] = 0;
+
+    for (int v : g[u]) {
+        if (v == f) continue;
+
+        dfs1(v, u);
+
+        siz[u] += siz[v];
+        weight[u] = std::max(weight[u], siz[v]);
+    }
+
+    // 顶上也算一棵子树
+    weight[u] = std::max(weight[u], n - siz[u]);
+
+    // 记录重心
+    if (centroid == 0) centroid = u;
+    else if (weight[u] < weight[centroid]) centroid = u;
+    // 重心相同，取编号小的
+    else if (weight[u] == weight[centroid] && u < centroid) centroid = u;
+}
+
+void dfs2(int u, int f) {
+    dep[u] = dep[f] + 1;
+
+    for (int v : g[u]) {
+        if (v == f) continue;
+
+        dfs2(v, u);
+    }
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n;
+
+    for (int i = 1, u, v; i < n; i++) {
+        cin >> u >> v;
+
+        g[u].emplace_back(v);
+        g[v].emplace_back(u);
+    }
+
+    dfs1(1, 0);
+    dfs2(centroid, 0);
+
+    cout << centroid << ' ' << std::accumulate(dep + 1, dep + 1 + n, 0) - n << endl;
+
+    return 0;
+}