python/TangDou/Topic/HuanGenDp/P1364_HuanGenDp.cpp

#include <bits/stdc++.h>
using namespace std;
#define LL long long
const int N = 1e5 + 10;
vector<int> g[N];
int a[N];
int dp[N], siz[N];
int ans = 1e9;
void dfs1(int u, int fa, int dep) {
    siz[u] = a[u];
    for (auto v : g[u]) {
        if (v == fa) continue;
        dfs1(v, u, dep + 1);
        siz[u] += siz[v];
    }
    dp[1] += dep * a[u]; // 先算出1点的总代价
}
void dfs2(int u, int fa) {
    for (auto v : g[u]) {
        if (v == fa) continue;
        dp[v] = dp[u] + siz[1] - siz[v] * 2;
        dfs2(v, u);
    }
    ans = min(ans, dp[u]);
}
int main() {
    int n;
    cin >> n;
    for (int i = 1; i <= n; i++) {
        cin >> a[i];
        int u, v;
        cin >> u >> v;
        if (u > 0) g[i].push_back(u), g[u].push_back(i);
        if (v > 0) g[i].push_back(v), g[v].push_back(i);
    }
    dfs1(1, 0, 0);
    dfs2(1, 0); // 换根
    cout << ans;
    return 0;
}