#include<stdio.h>
#include<string.h>
#define ll long long
const int N = 4e5+5;
//#define ll long long 
#define ull unsigned long long
#define lid (id << 1)
#define rid (id << 1 | 1)
struct Seg_node{
    int l, r;
    ll sum, mn, mx;
    ll lazy;
};
int a1[N];
Seg_node tr[N << 2];
void pushup(int id){
    tr[id].sum = tr[lid].sum + tr[rid].sum;
    tr[id].mn = min(tr[lid].mn, tr[rid].mn);
    tr[id].mx = max(tr[lid].mx, tr[rid].mx);
}
void pushdown(int id){
    if (tr[id].lazy){
        tr[lid].lazy += tr[id].lazy;
        tr[rid].lazy += tr[id].lazy;
        tr[lid].mn += tr[id].lazy;
        tr[rid].mn += tr[id].lazy;
        tr[lid].mx += tr[id].lazy;
        tr[rid].mx += tr[id].lazy;
        tr[lid].sum += tr[id].lazy * (tr[lid].r - tr[lid].l + 1);
        tr[rid].sum += tr[id].lazy * (tr[rid].r - tr[rid].l + 1);
        tr[id].lazy = 0;
    }
}
void build(int id, int l, int r){
    tr[id].l = l;
    tr[id].r = r;
    tr[id].lazy = 0;
    if (l >= r){
        tr[id].mx = a1[l];
        tr[id].mn = a1[l];
        tr[id].sum = a1[l];
        return;
    }
    int mid = (tr[id].l + tr[id].r) / 2;
    build(lid, l, mid);
    build(rid, mid + 1, r);
    pushup(id);
}	
void add(int id, int l, int r, ll val){
    if (l <= tr[id].l && tr[id].r <= r){
        tr[id].sum += val * (tr[id].r - tr[id].l + 1);
        tr[id].mx += val;
        tr[id].mn += val;
        tr[id].lazy += val;
        return;
    }
    pushdown(id);
    int mid = (tr[id].l + tr[id].r) >> 1;
    if (r <= mid) add(lid, l, r, val);
    else if (l > mid) add(rid, l, r, val);
    else add(lid, l, mid, val), add(rid, mid + 1, r, val);
    pushup(id);
}
void modify(int id, int x, ll y){
    if (tr[id].l == tr[id].r){
        tr[id].sum = tr[id].mx = tr[id].mx = y;
        return;
    }
    pushdown(id);
    int mid = (tr[id].l + tr[id].r) >> 1;
    if (x <= mid) modify(lid, x, y);
    else modify(rid, x, y);
    pushup(id);
}
ll query_sum(int id, int l, int r){
    if(tr[id].l>r||tr[id].r<l)return 0;
    if (l <= tr[id].l && tr[id].r <= r) return tr[id].sum;
    pushdown(id);
    int mid = (tr[id].l + tr[id].r) >> 1;
    if (r <= mid) return query_sum(lid, l, r);
    if (l > mid) return query_sum(rid, l, r);
    return query_sum(lid, l, mid) + query_sum(rid, mid + 1, r);
}
ll query_max(int id, int l, int r){
    if(tr[id].l>r||tr[id].r<l)return INT_MIN;
    if (l <= tr[id].l && tr[id].r <= r) return tr[id].mx;
    pushdown(id);
    int mid = (tr[id].l + tr[id].r) >> 1;
    if (r <= mid) return query_max(lid, l, r);
    if (l > mid) return query_max(rid, l, r);
    return max(query_max(lid, l, mid), query_max(rid, mid + 1, r));
}
ll query_min(int id, int l, int r){
    if (l <= tr[id].l && tr[id].r <= r) return tr[id].mn;
    pushdown(id);
    int mid = (tr[id].l + tr[id].r) >> 1;
    if (r <= mid) return query_min(lid, l, r);
    if (l > mid) return query_min(rid, l, r);
    return min(query_min(lid, l, mid), query_min(rid, mid + 1, r));
}
void modify1(int id, int l, int r, ll val){
    if (l <= tr[id].l && tr[id].r <= r){
        tr[id].sum = val * (tr[id].r - tr[id].l + 1);
        tr[id].mn = tr[id].mx = val;
        return;
    }
    pushdown(id);
    int mid = (tr[id].l + tr[id].r) >> 1;
    if (r <= mid) modify1(lid, l, r, val);
    else if (l > mid) modify1(rid, l, r, val);
    else modify1(lid, l, mid, val), modify1(rid, mid + 1, r, val);
}
ll n, q;
ll head[N << 1], nxt[N << 1], to[N << 1], val[N << 1], cccnnnttt, u[N << 1], v[N << 1], w[N << 1], val1[N << 1];
ll fa[N], dep[N], siz[N], hson[N], top[N], dfn[N], rnk[N], cnt;
ll a[N];
void add1(ll u, ll v, ll w){
	to[++cccnnnttt] = v;
	nxt[cccnnnttt] = head[u];
	val1[cccnnnttt] = w;
	head[u] = cccnnnttt;
}
void dfs1(ll u, ll f){
	hson[u] = -1;
	siz[u] = 1;
	ll maxson = -1;
	for (ll i = head[u];i;i = nxt[i]){
		ll v = to[i];
		if (v != f){
			dep[v] = dep[u] + 1;
			fa[v] = u;
			val[v] = val1[i];
			dfs1(v, u);
			siz[u] += siz[v];
			if (siz[v] > maxson) maxson = siz[v], hson[u] = v;
		}
	}
}
void dfs2(ll u, ll t){
	top[u] = t;
	dfn[u] = ++cnt;
	rnk[cnt] = u;
	a1[dfn[u] = val[u];
	if (hson[u] == -1) return;
	dfs2(hson[u], t);
	for (ll i = head[u];i;i = nxt[i]){
		ll v = to[i];
		if (v != hson[u] && v != fa[u]) dfs2(v, v);
	}
}
ll qrangesum(int x, int y){
	ll ans = 0;
	while (top[x] != top[y]){
		if (dep[top[x]] < dep[top[y]]) swap(x, y);
		ans += query_sum(1, dfn[top[x]], dfn[x]);
		x = fa[top[x]];
	}
	if (dep[x] > dep[y]) swap(x, y);
	ans += query_sum(1, dfn[x], dfn[y]);
	return ans;
}
ll qrangemax(int x, int y){
	ll ans = 0;
	while (top[x] != top[y]){
		if (dep[top[x]] < dep[top[y]]) swap(x, y);
		ans = max(ans, query_max(1, dfn[top[x]], dfn[x]));
		x = fa[top[x]];
	}
	if (dep[x] > dep[y]) swap(x, y);
	ans = max(ans, query_max(1, dfn[x] + 1, dfn[y]));
	return ans;
}
void addrange(int x, int y, ll k){
	while (top[x] != top[y]){
		if (dep[top[x]] < dep[top[y]]) swap(x, y);
		modify1(1, dfn[top[x]], dfn[x], k);
		x = fa[top[x]];
	}
	if (dep[x] > dep[y]) swap(x, y);
	modify1(1, dfn[x] + 1, dfn[y], k);
}
ll qsubtreesum(int x){
	return query_sum(1, dfn[x], dfn[x] + siz[x] - 1);
}
ll qsubtreemax(int x){
	return query_max(1, dfn[x], dfn[x] + siz[x] - 1);
}
void addsubtree(int x, ll k){
	add(1, dfn[x], dfn[x] + siz[x] - 1, k);
}
ll qnode(int x){
	return query_sum(1, dfn[x], dfn[x]);
}
void modifynode(int x, ll k){
	modify(1, dfn[x], k);
}
int main(){
	cin >> n;
	for (int i = 1;i < n;i++){
		cin >> u[i] >> v[i] >> w[i];
		add1(u[i], v[i], w[i]);
		add1(v[i], u[i], w[i]);
	}
	val[1] = 0;
	dep[1] = 1;
	dfs1(1, 0);
	dfs2(1, 1);
	build(1, 1, n);
	while (1){
		string s;
		int a, b;
		cin >> s;
		if (s == "DONE") break;
		cin >> a >> b;
		if (s == "CHANGE"){
			int V = v[a], U = u[a];
			if(dep[V]<dep[U])swap(V,U);
			modifynode(V, b);
		}
		else{
			cout << qrangemax(a, b) << '\n';
		}
	}
	return 0;
} 

洛谷IDE在struct seg_node报错，难道C没有结构体？

以及int a1[N] 错误：文件域中的动态可变的‘a1’