846. 树的重心(DFS\树的重心\树的遍历)

846. 树的重心

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

const int N = 1e5 + 10;

int h[N], e[N*2], ne[N*2], idx;
int n, res = INT_MAX;
bool st[N];

void add(int a, int b){
    e[idx] = b, ne[idx] = h[a], h[a] = idx++;
}
int dfs(int u){
    st[u] = 1;
    int sum = 1, ans = 0;
    for(int i = h[u]; i != -1; i = ne[i]){
        int j = e[i];
        if(!st[j]){
            int j = e[i];
            int t = dfs(j);
            ans = max(ans, t);
            sum += t;          
        }
    }
    ans = max(ans, n - sum);
    res = min(res, ans);
    
    return sum;
}
signed main(){
    memset(h, -1, sizeof h);
    cin >> n;
    for(int i = 1; i <= n - 1; ++i){
        int a, b; cin >> a >> b; add(a, b), add(b, a);
    }
    
    dfs(1);
    
    cout << res << endl;
    
    return 0;
}