poj1655

建树dfs

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
using namespace std;

#define maxn 20005

struct Edge
{
    int v, next;
} edge[maxn * 2];

int n, ecount;
int head[maxn];
int f[maxn];
int ans, ansi;
bool vis[maxn];

void addedge(int a, int b)
{
    edge[ecount].v = b;
    edge[ecount].next = head[a];
    head[a] = ecount;
    ecount++;
}

void input()
{
    memset(head, -1, sizeof(head));
    ecount = 0;
    scanf("%d", &n);
    for (int i = 0; i < n - 1; i++)
    {
        int a, b;
        scanf("%d%d", &a, &b);
        a--;
        b--;
        addedge(a, b);
        addedge(b, a);
    }
}

void dfs(int a)
{
    f[a] = 1;
    vis[a] = true;
    int x = 0;
    for (int i = head[a]; i != -1; i = edge[i].next)
        if (!vis[edge[i].v])
        {
            dfs(edge[i].v);
            f[a] += f[edge[i].v];
            x = max(x, f[edge[i].v]);
        }
    x = max(x, n - f[a]);
    if (x < ans)
    {
        ans = x;
        ansi = a;
    }
}

int main()
{
//    freopen("t.txt", "r", stdin);
    int t;
    scanf("%d", &t);
    while (t--)
    {
        input();
        ans = 0x3f3f3f3f;
        memset(vis, 0, sizeof(vis));
        dfs(0);
        printf("%d %d\n", ansi + 1, ans);
    }
    return 0;
}