SGU 134 Centroid【树的重心】

树的重心。递归求解即可。

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>
using namespace std;
#define N 16100
vector<int> g[N];
int n, cur, s[N], f[N];
void getroot(int now, int fa) {
    s[now] = 1;
    f[now] = 0;
    int u;
    for (int i=0; i<g[now].size(); i++)
        if ((u = g[now][i]) != fa) {
            getroot(u, now);
            s[now] += s[u];
            f[now] = max(f[now], s[u]);
        }
    f[now] = max(f[now], n-s[now]);
    if (f[now] < f[cur]) cur = now;
}
int main() {
    int a, b;
    scanf("%d", &n);
    for (int i=1; i<n; i++) {
        scanf("%d%d", &a, &b);
        g[a].push_back(b); g[b].push_back(a);
    }
    f[cur] = n;
    getroot(1, cur=0);
    vector<int> ans;
    for (int i=1; i<=n; i++) if (f[i] == f[cur]) ans.push_back(i);
    sort(ans.begin(), ans.end());
    printf("%d %d\n", f[cur], ans.size());
    printf("%d", ans[0]);
    for (int i=1; i<ans.size(); i++) printf(" %d", ans[i]);
    return 0;
}