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| #include <bits/stdc++.h>
const int MaxN = 500010;
struct edge
{
int next, to, dis;
};
struct node
{
int max;
int l, r;
};
edge e[MaxN << 1];
int n, cnt, dfsnum;
int a[MaxN], head[MaxN], dep[MaxN], fa[MaxN], size[MaxN];
int hson[MaxN], dfn[MaxN], top[MaxN], from[MaxN], to[MaxN], pre[MaxN];
struct SegmentTree
{
node t[MaxN << 2];
inline void pushup(int id) { t[id].max = std::max(t[id << 1].max, t[id << 1 | 1].max); }
inline void build(int id, int l, int r)
{
t[id].l = l, t[id].r = r;
if (l == r)
{
t[id].max = a[pre[l]];
return;
}
int mid = (l + r) >> 1;
build(id << 1, l, mid);
build(id << 1 | 1, mid + 1, r);
pushup(id);
}
inline void modify(int id, int l, int r, int val)
{
if (t[id].l > r || t[id].r < l)
return;
if (l <= t[id].l && t[id].r <= r)
{
t[id].max = val;
return;
}
modify(id << 1, l, r, val);
modify(id << 1 | 1, l, r, val);
pushup(id);
}
inline int query(int id, int l, int r)
{
if (l > t[id].r || r < t[id].l)
return 0;
if (l <= t[id].l && t[id].r <= r)
return t[id].max;
return std::max(query(id << 1, l, r), query(id << 1 | 1, l, r));
}
} T;
inline void add_edge(int u, int v, int d)
{
++cnt;
e[cnt].to = v;
e[cnt].dis = d;
e[cnt].next = head[u];
head[u] = cnt;
}
inline int read()
{
int x = 0;
char ch = getchar();
while (ch > '9' || ch < '0')
ch = getchar();
while (ch <= '9' && ch >= '0')
x = (x << 1) + (x << 3) + (ch ^ 48), ch = getchar();
return x;
}
inline void dfs1(int u, int f)
{
size[u] = 1;
for (int i = head[u]; i; i = e[i].next)
{
int v = e[i].to;
if (v == f)
continue;
fa[v] = u;
dep[v] = dep[u] + 1;
a[v] = e[i].dis;
dfs1(v, u);
size[u] += size[v];
if (size[hson[u]] < size[v])
hson[u] = v;
}
}
inline void dfs2(int u, int Top)
{
++dfsnum;
dfn[u] = dfsnum;
pre[dfsnum] = u;
top[u] = Top;
if (hson[u])
dfs2(hson[u], Top);
for (int i = head[u]; i; i = e[i].next)
{
int v = e[i].to;
if (v == fa[u] || v == hson[u])
continue;
dfs2(v, v);
}
}
inline void modify(int pos, int val) { T.modify(1, dfn[pos], dfn[pos], val); }
inline int query_chain(int u, int v)
{
int ans = 0;
if (dfn[u] < dfn[v])
std::swap(u, v);
while (top[u] != top[v])
{
if (dfn[u] < dfn[v])
std::swap(u, v);
ans = std::max(ans, T.query(1, dfn[top[u]], dfn[u]));
u = fa[top[u]];
}
if (dfn[u] < dfn[v])
std::swap(u, v);
ans = std::max(ans, T.query(1, dfn[v] + 1, dfn[u]));
return ans;
}
int main()
{
n = read();
for (int i = 1; i < n; i++)
{
int u, v, d;
scanf("%d%d%d", &u, &v, &d);
from[i] = u;
to[i] = v;
add_edge(u, v, d);
add_edge(v, u, d);
}
dep[1] = 1, fa[1] = 0;
dfs1(1, 0), dfs2(1, 1);
T.build(1, 1, n);
std::string op;
std::cin >> op;
while (op != "DONE")
{
if (op == "CHANGE")
{
int x = read(), val = read();
int u = from[x], v = to[x];
if (fa[v] == u)
std::swap(u, v);
modify(u, val);
}
else
{
int a = read(), b = read();
printf("%d\n", query_chain(a, b));
}
std::cin >> op;
}
return 0;
}
|