rt，只AC了最后两个点，感觉是线段树的问题

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>

using namespace std;

const int MAXN = 1e5 + 1e2;

int n, Q;
struct edge
{
    int to, next;
}e[MAXN];
int head[MAXN], cnt;

int fa[MAXN], d[MAXN], size[MAXN], hson[MAXN];
int TCS_cnt, dfn[MAXN], top[MAXN];

struct tree
{
    int l, r, depest, tag;
}t[MAXN << 2];

inline int read()
{
    int x = 0; char ch = getchar();
    while ( !isdigit(ch) ) ch = getchar();
    while ( isdigit(ch) ) { x = x * 10 + (ch - '0'); ch = getchar(); }
    return x;
}

void add (int u, int v) { e[++ cnt].to = v; e[cnt].next = head[u]; head[u] = cnt; }
void input()
{
    n = read(); Q = read();
    for (register int i = 1; i < n; i ++)
    {
        int u, v;
        u = read(); v = read();
        add (u, v);
    }
}

void dfs1_init() { d[1] = 1; }

void dfs1 (int u)
{
    size[u] = 1;
    for (register int i = head[u]; i; i = e[i].next)
    {
        int v = e[i].to;
        fa[v] = u;
        d[v] = d[u] + 1;
        dfs1 (v);
        size[u] += size[v];
        if (!hson[u] or size[v] > size[ hson[u] ]) hson[u] = v;
    }
}

void dfs2 (int u, int t)
{
    dfn[u] = ++ TCS_cnt;
    top[u] = t;
    if (!hson[u]) return;
    dfs2 (hson[u], t);
    for (register int i = head[u]; i; i = e[i].next)
    {
        int v = e[i].to;
        if (v != fa[u] and v != hson[u]) dfs2 (v, v);
    }
}

void build (int p, int l, int r)
{
    t[p].l = l, t[p].r = r, t[p].depest = 1;
    if (l == r) return;
    int mid = (l + r) >> 1;
    build (p << 1, l, mid); build (p << 1 | 1, mid + 1, r);
}

void spread (int p)
{
    if (!t[p].tag) return;
    if (d[t[p].tag] > d[t[p << 1].depest])
    {
        t[p << 1].depest = t[p].tag;
        if (d[t[p].tag] > d[t[p << 1].tag]) t[p << 1].tag = t[p].tag;
    }
    if (d[t[p].tag] > d[t[p << 1 | 1].depest])
    {
        t[p << 1 | 1].depest = t[p].tag;
        if (d[t[p].tag] > d[t[p << 1 | 1].tag]) t[p << 1 | 1].tag = t[p].tag;
    }
    t[p].tag = 0;
}
void SeT_update (int p, int l, int r, int k)
{
    if (l <= t[p].l and t[p].r <= r)
    {
        if (d[k] > d[t[p].depest])
        {
            t[p].depest = k;
            if (d[k] > d[t[p].tag]) t[p].tag = k;
        }
        return;
    }
    spread (p);
    int mid = (t[p].l + t[p].r) >> 1;
    if (l <= mid) SeT_update (p << 1, l, r, k);
    if (r > mid) SeT_update (p << 1 | 1, l, r, k);
    if (d[t[p << 1].depest] > d[t[p << 1 | 1].depest]) t[p].depest = t[p << 1].depest;
    else t[p].depest = t[p << 1 | 1].depest;
}
void TCS_update (int x)
{
    SeT_update (1, dfn[x], dfn[x] + size[x] - 1, x);
}
int SeT_query (int p, int l, int r)
{
    if (l <= t[p].l and t[p].r <= r) return t[p].depest;
    spread (p);
    int mid = (t[p].l + t[p].r) >> 1, res = -1;
    if (l <= mid) res = SeT_query (p << 1, l, r);
    if (r > mid)
    {
        int hhd = SeT_query (p << 1 | 1, l, r);
        if (res = -1 or d[res] < d[hhd]) res = hhd;
    }
    return res;
}
int TCS_query (int u, int v)
{
    int ans = -1;
    while (top[u] != top[v])
    {
        if (d[ top[v] ] < d[ top[u] ]) swap (u, v);
        ans = SeT_query (1, dfn[ top[v] ], dfn[v]);
        if (ans != -1) return ans;
        v = fa[ top[v] ];
    }
    if (d[v] < d[u]) swap (u, v);
    ans = SeT_query (1, dfn[u], dfn[v]);
    return ans;
}
void work()
{
    while (Q --)
    {
        char op; int x;
        cin >> op; x = read();
        if (op == 'C') TCS_update (x);
        else printf ("%d\n", TCS_query (1, x) );
    }
}

int main()
{
    input();
    dfs1_init();
    dfs1 (1);
    dfs2 (1, 1);
    build (1, 1, n);
    work();
    return 0;
}