点分树

struct BIT{
	int sz;
	vector<int> c;
	void build(int s){
		c.resize(s+1);
		sz=s;
	}
	int lowbit(int x){
		return x&(-x);
	}
	void add(int x,int y){
		x++;
		for(;x<=sz;x+=lowbit(x)) c[x]+=y;
	}
	int sum(int x){
		x++;
		int ans=0;x=min(x,sz);
		for(;x;x-=lowbit(x)) ans+=c[x];
		return ans;
	}
};
struct DFS{
	int sz[N],mxs[N],ct[N],fu[N];
	BIT c1[N],c2[N];
	int gt_rt(int x,int fa,int st){
		int q=x;
		mxs[x]=max(mxs[x],sz[st]-sz[x]);
		for(int i=h[x];i;i=d[i].n){
			int y=d[i].b;
			if(ct[y]||y==fa) continue;
			int p=gt_rt(y,x,st);
			if(mxs[p]<mxs[q]) q=p;
		}
		return q;
	}
	void dfs(int x,int fa){
		sz[x]=1,mxs[x]=0;
		for(int i=h[x];i;i=d[i].n){
			int y=d[i].b;
			if(y==fa||ct[y]) continue;
			dfs(y,x);
			sz[x]+=sz[y],mxs[x]=max(mxs[x],sz[y]);
		}
	}
	void build(int x){
		ct[x]=1,sz[x]++;
		c1[x].build(sz[x]),c2[x].build(sz[x]);
		for(int i=h[x];i;i=d[i].n){
			int y=d[i].b;
			if(ct[y]) continue;
			dfs(y,x);
			int rt=gt_rt(y,x,y);
			fu[rt]=x,sz[rt]=sz[y];build(rt);
		}
	}
	void pre(){
		mxs[0]=1e9;
		memset(ct,0,sizeof(ct));
		memset(fu,0,sizeof(fu));
		dfs(1,0);
		int rt=gt_rt(1,0,1);
		build(rt);
	}
	void jia(int x,int y){
		for(int i=x;i;i=fu[i]) c1[i].add(Tl.dis(x,i),y);
		for(int i=x;fu[i];i=fu[i]) c2[i].add(Tl.dis(x,fu[i]),y);
	}
	int he(int x,int y){
		int ans=c1[x].sum(y);
		for(int i=x;fu[i];i=fu[i]){
			int z=y-Tl.dis(x,fu[i]); 
			if(z<0) continue;
			ans+=c1[fu[i]].sum(z)-c2[i].sum(z);
		}
		return ans;
	}
}T;