C++ 代码

#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;

const int N = 100010, M = N * 2;

int n;
int h[N], e[M], ne[M], idx;
int ans = N;
bool st[N];

void add(int a, int b) {
    e[idx] = b, ne[idx] = h[a], h[a]= idx ++;
}
// 以u为根的子树中点的数量
int dfs(int u) {
    st[u] = true;

    int size = 0, sum = 1;

    for (int i = h[u]; i != -1; i = ne[i]) {
        int j = e[i];
        if (st[j]) continue;

        int s = dfs(j); // 用s表示当前子树的大小
        size = max(size, s);
        sum += s;
    }

    size = max(size, n - sum);
    ans  = min(ans, size);

    return sum;
}

int main() {
    scanf("%d", &n);

    memset(h, -1, sizeof h);

    for (int i = 0; i < n - 1; ++ i) {
        int a, b;
        scanf("%d%d", &a, &b);

        add(a, b), add(b, a);
    }

    dfs(1);

    printf("%d", ans);

    return 0;
}