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| #include <bits/stdc++.h>
using namespace std;
namespace TYC
{
typedef long long ll;
const int N = 366666 * 2 + 5, M = 20;
const ll INF = 0x3f3f3f3f3f3f3f3fLL;
int n, node_cnt, rot[N];
ll ans;
struct edge { int v, w; };
struct node { int son[2]; ll val; } tr[N * M];
namespace T1
{
int tot, size[N], Head[N], now[N];
ll dis[N];
vector<edge> T[N];
struct Edge { int to, next, w, vis; } E[N << 1];
inline void add(const int u, const int v, const int w)
{
static int ec = 1;
E[++ec] = {v, Head[u], w, 0};
Head[u] = ec;
E[++ec] = {u, Head[v], w, 0};
Head[v] = ec;
}
void buildtree(const int u, const int f)
{
for (auto p : T[u])
if (p.v != f)
{
dis[p.v] = dis[u] + p.w;
buildtree(p.v, u);
}
static vector<edge> son;
son.clear();
for (auto p : T[u])
if (p.v != f)
son.push_back(p);
int sz = int(son.size());
if (!sz)
return;
for (int i = 0; i < sz; i++)
add(tot + i + 1, son[i].v, son[i].w);
for (int i = 1; i < sz; i++)
add(tot + i, tot + i + 1, 0);
add(u, tot + 1, 0);
tot += sz;
}
void build()
{
tot = n;
for (int i = 1, u, v, w; i < n; i++)
{
scanf("%d%d%d", &u, &v, &w);
T[u].push_back({v, w});
T[v].push_back({u, w});
}
buildtree(1, 0);
for (int i = 1; i <= n; i++)
rot[i] = now[i] = ++node_cnt;
}
void getsize(const int u, const int f)
{
size[u] = 1;
for (int i = Head[u], v; i; i = E[i].next)
if (!E[i].vis && (v = E[i].to) != f)
{
getsize(v, u);
size[u] += size[v];
}
}
void getedge(const int u, const int f, const int sz, int &p)
{
for (int i = Head[u], v; i; i = E[i].next)
if (!E[i].vis && (v = E[i].to) != f)
{
if (max(size[v], sz - size[v]) < max(size[E[p].to], sz - size[E[p].to]))
p = i;
getedge(v, u, sz, p);
}
}
void dfs(const int u, const int f, const ll d, const int c)
{
if (u <= n)
{
tr[now[u]].son[c] = ++node_cnt;
tr[now[u] = node_cnt].val = d + dis[u];
}
for (int i = Head[u], v; i; i = E[i].next)
if (!E[i].vis && (v = E[i].to) != f)
dfs(v, u, d + E[i].w, c);
}
void solve(const int x)
{
getsize(x, 0);
if (size[x] == 1)
return;
int p = 0, u, v;
getedge(x, 0, size[x], p);
E[p].vis = E[p ^ 1].vis = 1;
dfs(u = E[p].to, 0, E[p].w, 0);
dfs(v = E[p ^ 1].to, 0, 0, 1);
solve(u);
solve(v);
}
}
namespace T2
{
ll res;
vector<edge> E[N];
void update(const int x, const int y)
{
if (x && y)
ans = max(ans, tr[x].val + tr[y].val - res);
}
void merge(int &x, const int y)
{
if (!x || !y)
return void(x = x + y);
tr[x].val = max(tr[x].val, tr[y].val);
update(tr[x].son[0], tr[y].son[1]);
update(tr[x].son[1], tr[y].son[0]);
merge(tr[x].son[0], tr[y].son[0]);
merge(tr[x].son[1], tr[y].son[1]);
}
void dfs(const int u, const int f, const ll d)
{
ans = max(ans, (T1::dis[u] - d) * 2);
for (auto p : E[u])
if (p.v != f)
{
dfs(p.v, u, d + p.w);
res = d * 2;
merge(rot[u], rot[p.v]);
}
}
void solve()
{
for (int i = 1, u, v, w; i < n; i++)
{
scanf("%d%d%d", &u, &v, &w);
E[u].push_back({v, w});
E[v].push_back({u, w});
}
dfs(1, 0, 0);
}
}
void work()
{
scanf("%d", &n);
T1::build();
T1::solve(1);
T2::solve();
printf("%lld\n", ans >> 1);
}
}
int main()
{
TYC::work();
return 0;
}
|
