我在整体二分的时候忘记在向右递归的时候重置树状数组，但是AC了：

#include<bits/stdc++.h>
using namespace std;
const int N=4e4+10,M=16;
vector<int> e[N];
int dep[N],sz[N],fa[N],son[N],top[N],dfn[N],ts;
int n,m,qm;
struct Plt//盘子
{
    int l1,r1,l2,r2,t;//类型
    int w;//权值
    bool operator<(const Plt &T)const
    {
        return w<T.w;
    }
}p[N];
struct Qry
{
    int x,y,k;
    int id;
    int res,dt;
}q[N],lq[N],rq[N];
struct Mdf
{
    int x,y,v,id;//坐标，权值，id
    bool operator<(const Mdf &T)const
    {
        if(x!=T.x) return x<T.x;
        return id<T.id;
    }
};
struct Bit
{
    int tr[N];
    int lowbit(int x)
    {
        return x&-x;
    }
    void add(int x,int c)
    {
        for(int i=x;i<=n;i+=lowbit(i)) tr[i]+=c;
    }
    int sum(int x)
    {
        int res=0;
        for(int i=x;i;i-=lowbit(i)) res+=tr[i];
        return res;
    }
}Bit;
int ans[N];

void dfs1(int u,int p)
{
    dep[u]=dep[p]+1,sz[u]=1,fa[u]=p;
    for(auto v:e[u])
    {
        if(v==p) continue;
        dfs1(v,u);
        sz[u]+=sz[v];
        if(sz[v]>sz[son[u]]) son[u]=v;
    }
}

void dfs2(int u,int t)
{
    top[u]=t,dfn[u]=++ts;
    if(son[u]) dfs2(son[u],t);
    for(auto v:e[u])
    {
        if(v==fa[u]||v==son[u]) continue;
        dfs2(v,v);
    }
}

int find(int u,int v)
{
    while(top[u]!=top[v])
    {
        u=top[u];
        if(fa[u]==v) return u;
        u=fa[u];
    }
    return son[v];
}

void add_M(vector<Mdf> &V,int l1,int r1,int l2,int r2,int c)
{
    V.push_back({l1,l2,c,0});
    if(r2+1<=n) V.push_back({l1,r2+1,-c,0});
    if(r1+1<=n) V.push_back({r1+1,l2,-c,0});
    if(r1+1<=n&&r2+1<=n) V.push_back({r1+1,r2+1,c,0});
}

void add_q(vector<Mdf> &V,int t,int l1,int r1,int l2,int r2,int c)
{
    if(t==1) add_M(V,1,l2-1,l1,r1,c),add_M(V,l1,r1,r2+1,n,c);
    else add_M(V,l1,r1,l2,r2,c);
}

void Sum(vector<Mdf> &V,int x,int y,int id)
{
    V.push_back({x,y,0,id});
}

void solve(int L,int R,int l,int r)//决策区间，询问区间
{
    if(L>=R)
    {
        for(int i=l;i<=r;i++) ans[q[i].id]=L;
        return;
    }
    
    int mid=L+R>>1,ln=0,rn=0;
    vector<Mdf> Sc;
    
    for(int i=L;i<=mid;i++) add_q(Sc,p[i].t,p[i].l1,p[i].r1,p[i].l2,p[i].r2,1);
    
    for(int i=l;i<=r;i++)
    {
        int x=q[i].x,y=q[i].y,k=q[i].k;
        Sum(Sc,x,y,i);
    }
    
    sort(Sc.begin(),Sc.end());
    
    for(auto T:Sc)
    {
        int x=T.x,y=T.y,v=T.v,id=T.id;
        if(!id) Bit.add(y,v);
        else q[id].dt=Bit.sum(y),q[id].res+=q[id].dt;
    }
    
    for(int i=l;i<=r;i++)
    {
        if(q[i].res>=q[i].k) lq[ln++]=q[i];
        else rq[rn++]=q[i];
    }
    
    for(int i=0,j=l;i<ln;i++,j++) q[j]=lq[i];
	for(int i=0,j=l+ln;i<rn;i++,j++) q[j]=rq[i];
	
	solve(mid+1,R,l+ln,r);
	
	for(auto T:Sc)
	{
		int x=T.x,y=T.y,v=T.v,id=T.id;
		if(!id) Bit.add(y,-v);
	}
	
	for(int i=l;i<=r;i++) q[i].res-=q[i].dt,q[i].dt=0;
	
	solve(L,mid,l,l+ln-1);
}

signed main()
{
	ios::sync_with_stdio(false),cin.tie(0),cout.tie(0);
	
    cin>>n>>m>>qm;
    for(int i=1,a,b;i<n;i++) 
    {
        cin>>a>>b;
        e[a].push_back(b),e[b].push_back(a);
    }
    
    dfs1(1,0);
    dfs2(1,1);
    
    for(int i=1,u,v,l1,l2,r1,r2,t,w;i<=m;i++)
    {
        cin>>u>>v>>w;
        if(dfn[u]<dfn[v]) swap(u,v);
        if(dfn[v]<dfn[u]&&dfn[v]+sz[v]>dfn[u])//v是u的祖先
        {
            l1=dfn[u],r1=dfn[u]+sz[u]-1;
            int x=find(u,v);
            l2=dfn[x],r2=dfn[x]+sz[x]-1;
            t=1;
        }
        else
        {   
            l1=dfn[v],r1=dfn[v]+sz[v]-1;
            l2=dfn[u],r2=dfn[u]+sz[u]-1;
            t=2;
        }
        p[i]={l1,r1,l2,r2,t,w};
    }
    
    sort(p+1,p+1+m);
    
    for(int i=1,u,v,k;i<=qm;i++)
    {
        cin>>u>>v>>k;
        if(dfn[u]>dfn[v]) swap(u,v);
        q[i]={dfn[u],dfn[v],k,i,0};
    }
    
    solve(1,m,1,qm);
    
    for(int i=1;i<=qm;i++) cout<<p[ans[i]].w<<"\n";
    
    return 0;
}

然后我意识到问题了之后改过来，显然也AC了。

为啥不清空也能过，求大佬指教