python/TangDou/Topic/HuanGenDp/CF1187E.cpp

#include <bits/stdc++.h>
using namespace std;
const int N = 200010, M = N << 1;
#define int long long
#define endl "\n"

// 链式前向星
int e[M], h[N], idx, w[M], ne[M];
void add(int a, int b, int c = 0) {
    e[idx] = b, ne[idx] = h[a], w[idx] = c, h[a] = idx++;
}

int n;
int sz[N];
int f[N];
void dfs(int u, int fa) {
    sz[u] = 1;

    for (int i = h[u]; ~i; i = ne[i]) {
        int v = e[i];
        if (v != fa) {
            dfs(v, u);
            sz[u] += sz[v];
        }
    }
}
void dp(int u, int fa) {
    for (int i = h[u]; ~i; i = ne[i]) {
        int v = e[i];
        if (v != fa) {
            f[v] = f[u] + sz[1] - 2 * sz[v];
            dp(v, u);
        }
    }
}

signed main() {
    // 初始化链式前向星
    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, 0);

    for (int i = 1; i <= n; i++) f[1] += sz[i];

    dp(1, 0);

    int ans = -0x3f;
    for (int i = 1; i <= n; i++) ans = max(ans, f[i]);

    cout << ans << endl;
}