样例通过但0pts WA求条

#include<bits/stdc++.h>
#define int long long
using namespace std;

const int MAXN = 5e5 + 1;

int n, m, q, r, p, a[MAXN], s[MAXN], maxn[MAXN], lazy[MAXN];
int cnt, fa[MAXN], dep[MAXN], siz[MAXN], dfn[MAXN], son[MAXN], top[MAXN], seg[MAXN], ed[MAXN];
vector<int> c[MAXN];
struct EDGE {
    int x, y, z;
}edge[MAXN];
void dfs1(int x, int f) {
    dep[x] = dep[f] + 1;
    fa[x] = f;
    siz[x] = 1;
    for(int i = 0; i < c[x].size(); i++) {
        int y = c[x][i];
        if(y == f) {
            continue;
        }
        dfs1(y, x);
        siz[x] += siz[y];
        if(siz[y] > siz[son[x]]) {
            son[x] = y;
        }
    }
}

void dfs2(int x, int tp) {
    dfn[x] = ++cnt;
    seg[cnt] = x;
    top[x] = tp;
    if(son[x]) {
        dfs2(son[x], tp);
    }
    for(int i = 0; i < c[x].size(); i++) {
        if(c[x][i] != fa[x] && c[x][i] != son[x]) {
            dfs2(c[x][i], c[x][i]);
        }
    }
    ed[x] = cnt;
}

void push_up(int x) {
    maxn[x] = max(maxn[x * 2], maxn[x * 2 + 1]);
}

void build(int x, int l, int r) {
    if(l == r) {
        maxn[x] = a[l];
        return;
    }
    int mid = (l + r) / 2;
    build(x * 2, l, mid);
    build(x * 2 + 1, mid + 1, r);
    push_up(x);
}

void update(int L, int R, int l, int r, int k, int c) {
    if(l >= L && r <= R) {
		maxn[k] = c;
		return; 
    }
    int mid = (l + r) / 2;
    if(L <= mid) {
        update(L, R, l, mid, k * 2, c);
    }
    if(mid < R) {
        update(L, R, mid + 1, r, k * 2 + 1, c);
    }
    push_up(k);
}

int query_max(int L, int R, int l, int r, int k) {
    if(L > R) {
        return 0;
    }
    if(l >= L && r <= R) {
        return maxn[k];
    }
    int mid = (l + r) / 2, res = 0;
    if(L <= mid) {
        res = max(res, query_max(L, R, l, mid, k * 2));
    }
    if(mid < R) {
        res = max(res, query_max(L, R, mid + 1, r, k * 2 + 1));
    }
    return res;
}
int LCA_max(int x, int y) {
    int res = 0;
    while(top[x] != top[y]) {
        if(dep[top[x]] > dep[top[y]]) {
            res = max(res, query_max(dfn[top[x]], dfn[x], 1, n, 1));
            x = fa[top[x]];
        }
        else {
            res = max(res, query_max(dfn[top[y]], dfn[y], 1, n, 1));
            y = fa[top[y]];
        }
    }
    if(dfn[x] > dfn[y]) {
        swap(x, y);
    }
    res = max(res, query_max(dfn[x] + 1, dfn[y], 1, n, 1));
    return res;
}

signed main() {
//    ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
    cin >> n;
    for(int i = 1, x, y, z; i < n; i++) {
        cin >> x >> y >> z;
        c[x].push_back(y);
        c[y].push_back(x);
        edge[i] = {x, y, z};
    }
    dfs1(1, 0);
    dfs2(1, 1);
    for(int i = 1; i < n; i++) {
        int x = edge[i].x, y = edge[i].y, z = edge[i].z;
        if(dep[x] < dep[y]) {
            swap(x, y);
        }
        a[x] = z;
    }
    build(1, 1, n);
    while(1) {
        string op;
        int x, y;
        cin >> op;
        if(op == "CHANGE") {
            int i, t;
            cin >> i >> t;
            x = edge[i].x, y = edge[i].y;
            if(dep[x] < dep[y]) {
                swap(x, y);
            }
            update(dfn[x], dfn[x], 1, n, 1, t);
        }
        else if(op == "DONE") {
            return 0;
        }
        else {
            cin >> x >> y;
            cout << LCA_max(x, y) << "\n";
        }
    }
    return 0;
}