$RT$，T 炸了 7 个点，开 C++20 O2 快读之后是 6 个，应该没有写成随机剖分

#include <stdio.h>
#include <string.h>
#include <limits.h>
#include <algorithm>

using std::max;
const int N = 2e5 + 5;

inline int fread()
{
    int n = 0;
    char c = getchar();
    while (c < '0' || c > '9') c = getchar();
    while ('0' <= c && c <= '9') n = (n << 3) + (n << 1) + c - '0', c = getchar();
    return n;
}

#ifdef ONLINE_JUDGE
#define debug(...) 0
#else
#define debug printf
#endif

struct node
{
    int l, r;
    int val;
};
struct segtree
{
    node a[N << 2];

#   define u a[i]
#   define lc a[i << 1]
#   define rc a[i << 1 | 1]
#   define mid (u.l + u.r) >> 1
#   define len(v) (v.r - v.l)

    inline void pushup(int i)
    {
        u.val = max(lc.val, rc.val);
    }

    inline void build(int i, int l, int r)
    {
        u.l = l, u.r = r;
        if (len(u) == 1)
        {
            u.val = 0;
            return;
        }
        build(i << 1, l, mid);
        build(i << 1 | 1, mid, r);
        pushup(i);
    }

    inline void modify(int i, int x, int k)
    {
        if (x < u.l || x >= u.r)
            return;
        if (len(u) == 1)
        {
            u.val = k;
            return;
        }
        if (x < mid) modify(i << 1, x, k);
        else modify(i << 1 | 1, x, k);
        pushup(i);
    }

    inline int query(int i, int l, int r)
    {
        if (r <= u.l || l >= u.r)
            return INT_MIN;
        if (l <= u.l && r >= u.r)
            return u.val;
        return max(query(i << 1, l, r), query(i << 1 | 1, l, r));
    }

#   undef u
#   undef lc
#   undef rc
#   undef mid
#   undef len
}
QwQ;

struct edge
{
    int u, v, w, next;
}
e[N << 1]; int cnt, head[N];

inline void add_edge(int u, int v, int w)
{
    e[cnt].u = u, e[cnt].v = v, e[cnt].w = w, e[cnt].next = head[u];
    head[u] = cnt++;
}

int depth[N], father[N], size[N], hson[N];
int dfn[N], top[N], dfscnt;

inline void dfs1(int u, int f)
{
    depth[u] = depth[f] + 1;
    father[u] = f;
    size[u] = 1;

    int qwq = 0;
    for (int i = head[u]; ~i; i = e[i].next)
        if (e[i].v != f)
        {
            int v = e[i].v;
            dfs1(v, u); size[u] += size[v];
            if (size[v] > qwq) qwq = size[v], hson[u] = v;
        }
    debug("hson[%d] = %d\n", u, hson[u]);
}

inline void dfs2(int u, int f)
{
    dfn[u] = dfscnt++;
    top[u] = f;
    if (size[u] == 1) return;

    dfs2(hson[u], hson[u]);
    for (int i = head[u]; ~i; i = e[i].next)
        if (e[i].v != father[u] && e[i].v != hson[u])
            dfs2(e[i].v, e[i].v);
}

inline void edge_modify(int u, int k)
{
    QwQ.modify(1, dfn[u], k);
}

inline int chain_query(int u, int v)
{
    int ans = INT_MIN;
    while (top[u] != top[v])
    {
        if (depth[top[u]] < depth[top[v]])
            std::swap(u, v);
        ans = max(ans, QwQ.query(1, dfn[top[u]], dfn[u] + 1));
        u = father[top[u]];
    }
    if (depth[u] < depth[v])
        std::swap(u, v);
    ans = max(ans, QwQ.query(1, dfn[v] + 1, dfn[u] + 1));
    return ans;
}

int cat[N], lhq[N], chtholly;
// cat[i]: 第 i 条边对应着 e[几]
// lhq[i]: 第 i 条边深度比较深的那个

int main()
{
    memset(head, -1, sizeof head);
    
    int n;
    n = fread();
    for (int i = 0; i < n - 1; i++)
    {
        int u, v, w;
        u = fread(), v = fread(), w = fread();
        cat[++chtholly] = cnt;
        add_edge(u, v, w), add_edge(v, u, w);
    }
    dfs1(1, 0);
    dfs2(1, 1);
    
    QwQ.build(1, 0, n);
    for (int i = 1; i < n; i++)
    {
        int qwq = cat[i], u = e[qwq].u, v = e[qwq].v;
        debug("qwq = %d, u = %d, v = %d, depth[u] = %d, depth[v] = %d\n", qwq, u, v, depth[u], depth[v]);
        if (depth[u] < depth[v])
            std::swap(u, v);
        lhq[i] = u; edge_modify(u, e[qwq].w);
        debug("cat[%d] = %d, lhq[%d] = %d\n", i, cat[i], i, lhq[i]);
    }

    while (true)
    {
        char op[114]; scanf(" %s", op);
        if (op[0] == 'C')
        {
            int x, t;
            x = fread(), t = fread();
            edge_modify(lhq[x], t);
        }
        if (op[0] == 'Q')
        {
            int u, v;
            u = fread(), v = fread();
            if (u == v) printf("0\n");
            else printf("%d\n", chain_query(u, v));
        }
        if (op[0] == 'D') break;
    }
    return 0;
}