POJ 1655 Balancing Act[树的重心/树形dp]

#include "stdio.h"
#include "algorithm"
#include "string.h"
using namespace std;
const int INF = 0x3f3f3f3f;
const int maxn = 20000 + 10;
bool vis[maxn];
struct edge {
    int to, next;
} e[maxn*2];
int n, num[maxn];
int size, cur;
int tot = 0;
int head[maxn];
void add_edge(int u, int v) {
    e[tot].to = v; e[tot].next = head[u];
    head[u] = tot++;
}
void dfs(int u) {
    num[u] = 0;
    int tr = 0;
    vis[u] = true;
    for (int i = head[u]; i != -1; i = e[i].next) {
        int v = e[i].to;
        if (vis[v]) continue;
        dfs(v);
        num[u] += num[v] + 1;
        tr = max(num[v] + 1, tr);
    } 
    tr = max(n - num[u] - 1, tr); //剩下那棵树的大小
    if (tr < size || tr == size && cur > u) { //答案还要编号节点最小
        size = tr; cur = u;
    }
}
void init() {
    memset(vis, false, sizeof(vis));
    memset(head, -1, sizeof(head));
    tot = 0; size = INF;
}
int main(int argc, char const *argv[])
{
    int T;
    scanf("%d", &T);
    while (T--) {
        init();
        scanf("%d", &n);
        for (int i = 0; i < n-1; i++) {
            int u, v;
            scanf("%d%d", &u, &v); add_edge(u, v);
            add_edge(v, u);
        }
        dfs(1);
        printf("%d %d\n", cur, size);
    }
    return 0;
}