树的重心 POJ_1655

//#include <bits/stdc++.h>

#include <iostream>
#include <vector>

using namespace std;

int N;                // 1<= N <= 20000
const int maxn = 20000;
vector<int> tree[maxn + 5];           // tree[i]表示节点i的相邻节点
int d[maxn + 5];                // d[i]表示以i为根的子树的节点个数

#define INF 10000000

int minNode;
int minBalance;

void dfs(int node, int parent) // node and its parent
{
    d[node] = 1; // the node itself
    int maxSubTree = 0; // subtree that has the most number of nodes
    for (int i = 0; i < tree[node].size(); i++) {
        int son = tree[node][i];
        if (son != parent) {
            dfs(son, node);
            d[node] += d[son];
            maxSubTree = max(maxSubTree, d[son]);
        }
    }
    maxSubTree = max(maxSubTree, N - d[node]); // "upside substree with (N - d[node]) nodes"

    if (maxSubTree < minBalance){
        minBalance = maxSubTree;
        minNode = node;
    }
}

int main()
{
    int t;
    cin >> t;
    while (t--){
        cin >> N;

        for (int i = 1; i <= N - 1; i++){
            tree[i].clear();
        }

        for (int i = 1; i <= N-1; i++){
            int u, v;
            cin >> u >> v;
            tree[u].push_back(v);
            tree[v].push_back(u);
        }

        minNode = 0;
        minBalance = INF;

        dfs(1, 0);                // fist node as root
        cout << minNode << " " << minBalance << endl;
    }

    return 0;
}