求助MLE

只A了1个点

 #include<bits/stdc++.h>
using namespace std;
int t,n,cnt,s[100010],pre[100010],m,cnt1,dep[100010],f[100010],siz[100010];
int tree[400010],son[100010],top[100010],id[100010],head[100010],val[100010];
string st;
struct nodd{
    int to,nxt,val;
}edge[200010];
struct node{
    int u,v;
}a[200010];
void add(int u,int v,int w){
    edge[++cnt].to=v;
    edge[cnt].nxt=head[u];
    edge[cnt].val=w;
    head[u]=cnt;
}
void dfs1(int now,int fa){
    dep[now]=dep[fa]+1;
    siz[now]=1;
    f[now]=fa;
    for(int i=head[now];i;i=edge[i].nxt){
        int v=edge[i].to;
        if(v==fa)continue;
        dfs1(v,now);
        val[v]=edge[i].val;
        siz[now]+=siz[v];
        if(siz[v]>siz[son[now]])son[now]=v;
    }
}
void dfs2(int now,int tp){
    top[now]=tp;
    id[now]=++cnt1;
    pre[cnt1]=now;
    if(son[now])dfs2(son[now],tp);
    for(int i=head[now];i;i=edge[i].nxt){
        int v=edge[i].to;
        if(v==f[now]||v==son[now])continue;
        dfs2(v,v);
    }
}
void pushup(int o){
    tree[o]=max(tree[o*2],tree[o*2+1]);
}
void build(int o,int l,int r){
    if(l==r){
        tree[o]=val[pre[l]];
        return;
    }
    int mid=(l+r)>>1;
    build(o*2,l,mid);
    build(o*2+1,mid+1,r);
    pushup(o);
}
void change(int o,int l,int r,int pos,int v){
    if(l==r){
        tree[o]=v;
        return;
    }
    int mid=(l+r)>>1;
    if(pos<=mid)change(o*2,l,mid,pos,v);
    else change(o*2+1,mid+1,r,pos,v);
    pushup(o);
}
int query1(int o,int l,int r,int L,int R){
    if(L<=l&&r<=R)return tree[o];
    int mid=(l+r)>>1;
    int ans=0;
    if(L<=mid)ans=max(ans,query1(o*2,l,mid,L,R));
    if(R>mid)ans=max(ans,query1(o*2+1,mid+1,r,L,R));
    return ans;
}
int query(int u,int v){
    if(u==v)return 0;
    int ans=0;
    while(top[u]!=top[v]){
        if(dep[u]<dep[v])swap(u,v);
        ans=max(ans,query1(1,1,n,id[top[u]],id[u]));
        u=f[top[u]];
    }
    if(dep[u]>dep[v])swap(u,v);
    ans=max(ans,query1(1,1,n,id[u]+1,id[v]));
    return ans;
}
signed main(){
    scanf("%d",&n);
    for(int i=1;i<n;i++){
        int u,v,w;
        scanf("%d%d%d",&u,&v,&w);
        add(u,v,w);
        add(v,u,w);
        a[i].u=u,a[i].v=v;
    }
    dfs1(1,0);
    dfs2(1,1);
    build(1,1,n);
    while(cin>>st&&st!="DONE"){
        if(st=="CHANGE"){
            int x,y;
            scanf("%d%d",&x,&y);
            int u=a[x].u,v=a[x].v;
            if(v==f[u])swap(u,v);
            change(1,1,n,id[v],y);
        }
        else{
            int u,v;
            scanf("%d%d",&u,&v);
            printf("%d\n",query(u,v));
        }
    }
    return 0;
}