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| #include <cstdio>
#include <algorithm>
using namespace std;
const int N = 1e5 + 10, M = 2e5 + 10;
int n, w[N], d[N], p[N], sz[N], son[N];
int idx = -1, hd[N], nxt[M], edg[M], wt[M], dir[M];
int stmp, dfn[N], rnk[N], top[N];
struct Node
{
int mx;
int l, r;
} tr[N << 2];
void pushup(int x)
{
tr[x].mx = max(tr[x << 1].mx, tr[x << 1 | 1].mx);
}
void build(int x, int l, int r)
{
tr[x].l = l;
tr[x].r = r;
if (l == r)
{
tr[x].mx = w[rnk[l]];
return;
}
int mid = l + r >> 1;
build(x << 1, l, mid);
build(x << 1 | 1, mid + 1, r);
pushup(x);
}
void modify(int x, int t, int k)
{
if (tr[x].l == tr[x].r)
{
tr[x].mx = k;
return;
}
int mid = tr[x].l + tr[x].r >> 1;
if (t <= mid)
modify(x << 1, t, k);
else
modify(x << 1 | 1, t, k);
pushup(x);
}
int query(int x, int l, int r)
{
if (tr[x].l >= l && tr[x].r <= r)
return tr[x].mx;
int res = 0;
int mid = tr[x].l + tr[x].r >> 1;
if (l <= mid)
res = max(res, query(x << 1, l, r));
if (r > mid)
res = max(res, query(x << 1 | 1, l, r));
return res;
}
void dfs1(int x)
{
sz[x] = 1;
son[x] = -1;
for (int i = hd[x]; ~i; i = nxt[i])
if (!d[edg[i]])
{
d[edg[i]] = d[x] + 1;
p[edg[i]] = x;
dir[i] = dir[i ^ 1] = edg[i];
w[edg[i]] = wt[i];
dfs1(edg[i]);
sz[x] += sz[edg[i]];
if (son[x] == -1 || sz[edg[i]] > sz[son[x]])
son[x] = edg[i];
}
}
void dfs2(int x, int t)
{
top[x] = t;
dfn[x] = ++stmp;
rnk[stmp] = x;
if (son[x] == -1)
return;
dfs2(son[x], t);
for (int i = hd[x]; ~i; i = nxt[i])
if (edg[i] != son[x] && edg[i] != p[x])
dfs2(edg[i], edg[i]);
}
void add(int a, int b, int c)
{
nxt[++idx] = hd[a];
hd[a] = idx;
edg[idx] = b;
wt[idx] = c;
}
int queryPath(int x, int y)
{
int res = 0;
while (top[x] != top[y])
{
if (d[top[x]] < d[top[y]])
swap(x, y);
res = max(res, query(1, dfn[top[x]], dfn[x]));
x = p[top[x]];
}
if (x == y)
return res;
if (d[x] > d[y])
swap(x, y);
return max(res, query(1, dfn[x] + 1, dfn[y]));
}
int main()
{
scanf("%d", &n);
for (int i = 1; i <= n; i++)
hd[i] = -1;
for (int i = 1, a, b, c; i < n; i++)
{
scanf("%d%d%d", &a, &b, &c);
add(a, b, c);
add(b, a, c);
}
d[1] = 1;
dfs1(1);
dfs2(1, 1);
build(1, 2, n);
char op[10];
while (~scanf("%s", op))
{
if (op[0] == 'D')
break;
if (op[0] == 'C')
{
int t, k;
scanf("%d%d", &t, &k);
modify(1, dfn[dir[t - 1 << 1]], k);
}
if (op[0] == 'Q')
{
int x, y;
scanf("%d%d", &x, &y);
printf("%d\n", queryPath(x, y));
}
}
return 0;
}
|