题目

代码

#include <bits/stdc++.h>
using namespace std;
const int N = 1e5+10, M = N*2;
int h[N], e[M], ne[M], idx;
int n;
int ans = 2e9;
bool st[N];
void add(int a, int b)  // 添加一条边a->b
{
    e[idx] = b, ne[idx] = h[a], h[a] = idx ++ ;
}
int dfs(int u)
{
    int maxx = 0; int sz = 0; st[u] = true;
    
    for(int i = h[u]; ~i; i = ne[i])
    {
        int j = e[i];
        if(st[j]) continue;
        int s = dfs(j);
        maxx = max(maxx, s);
        sz += s;
    }
    
    maxx = max(maxx, n-sz-1);
    ans = min(ans, maxx);
    
    return sz+1;
}
int main()
{
    cin >> n;
    
    memset(h, -1, sizeof h);
    for(int i = 0; i < n-1; i++)
    {
        int a, b;
        cin >> a >> b;
        add(a, b);
        add(b, a);
    }
    
    dfs(1);
    
    cout << ans;
}

注意