st表lca

struct Lca{
	int tot=0;
	int dep[N],pos[N],lca[N*2][20],lg[N*2];
	void pre(int x,int fa){
		dep[x]=dep[fa]+1,pos[x]=++tot,lca[tot][0]=x;
		for(int i=h[x];i;i=d[i].n){
			int y=d[i].b;
			if(y==fa) continue;
			pre(y,x);lca[++tot][0]=x;
		}
	}
	int xiao(int x,int y){
		if(dep[x]<dep[y]) return x;
		return y;
	}
	void ST(){
		lg[0]=-1;
		for(int i=1;i<=tot;i++) lg[i]=lg[i/2]+1;
		for(int j=1;j<=19;j++){
			for(int i=1;i+(1<<j)-1<=tot;i++) lca[i][j]=xiao(lca[i][j-1],lca[i+(1<<(j-1))][j-1]);
		}
	}
	int LCA(int x,int y){
		if(pos[x]>pos[y]) swap(x,y);
		int len=pos[y]-pos[x]+1;
		return xiao(lca[pos[x]][lg[len]],lca[pos[y]-(1<<lg[len])+1][lg[len]]);
	}	
	int dis(int x,int y){
		int _lca=LCA(x,y);
		return dep[x]+dep[y]-2*dep[_lca];
	}
}Tl;