python/TangDou/Topic/HuanGenDp/POJ3585.cpp

#include <iostream>
#include <cstdio>
#include <vector>
#include <cstring>
using namespace std;
const int N = 2e5 + 10, M = N << 1;

int n, du[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 d[N], f[N];

void dfs1(int u, int fa) {
    for (int i = h[u]; ~i; i = ne[i]) {
        int v = e[i];
        if (v == fa) continue;
        dfs1(v, u);
        if (du[v] == 1)
            d[u] += w[i];
        else
            d[u] += min(d[v], w[i]);
    }
    return;
}
void dfs2(int u, int fa) {
    for (int i = h[u]; ~i; i = ne[i]) {
        int v = e[i];
        if (v == fa) continue;
        if (du[u] == 1)
            f[v] = d[v] + w[i];
        else
            f[v] = d[v] + min(f[u] - min(d[v], w[i]), w[i]);
        dfs2(v, u);
    }
    return;
}

int main() {
    // 加快读入
    ios::sync_with_stdio(false), cin.tie(0);
    int T;
    cin >> T;
    while (T--) {
        // 初始化链式前向星
        memset(h, -1, sizeof h);
        idx = 0;
        memset(du, 0, sizeof du);
        memset(d, 0, sizeof d);
        memset(f, 0, sizeof f);

        cin >> n;

        int a, b, c;
        for (int i = 1; i < n; i++) { // 树，n-1条无向边
            cin >> a >> b >> c;
            add(a, b, c), add(b, a, c);
            du[a]++, du[b]++; // 记录入度,无向图就不谈入度和出度了
        }

        dfs1(1, 0);
        f[1] = d[1];
        dfs2(1, 0);

        int ans = 0;
        for (int i = 1; i <= n; i++) ans = max(ans, f[i]);
        cout << ans << endl;
    }
    return 0;
}