照着OI-wiki上敲的，不知道哪里有错。

#include<bits/stdc++.h>
using namespace std;

int n;
int h[100010], e[200010], ne[200010], idx = 0;
int sizee[100010], weight[100010], ans[2], cnt, st[100010], res = 0x3f3f3f3f;

void add(int a, int b)
{
    e[idx] = b;
    ne[idx] = h[a];
    h[a] = idx;
    idx++;
}

int dfs(int u)
{
    st[u] = 1;
     sizee[u] = 1;
    weight[u] = 0;
    
    for(int i = h[u];i != -1;i = ne[i])
    {
        int j = e[i];
        if(!st[j])
        dfs(j);
        sizee[u] += sizee[j];
        weight[u] = max(weight[u], sizee[j]);
    }
    
    weight[u] = max(weight[u], n - sizee[u]);
    if(weight[u] <= n / 2);
    ans[++cnt] = u;
}

int main()
{
    memset(h, -1, sizeof(h));
    
    cin >> n;
    for(int i = 1;i < n;i++)
    {
        int a, b;
        cin >> a >> b;
        add(a, b);
        add(b, a);
    }
    
    dfs(1);
    
    
    return 0;
}