为什么所有人的 B 做法都是 Hash 啊

#include<bits/stdc++.h>
#define int long long

using namespace std;

const int N=300005;

int n,m,l,k;
int op[N];
pair<int,int> nodes[N],qst[N];

int siz[N],fa[N],Fa[N],cnt[N];vector<int> vec[N];
int dfs(int u,int father) {
	int v=u+1;siz[u]=(1ll<<(n-nodes[u].second+1))-1;Fa[u]=fa[u]=father;
	while(v<=l && (nodes[u].first^nodes[v].first)<(k>>nodes[u].second)) {
		vec[u].push_back(v);
		v=dfs(v,u);
	}
	return v;
}

int find(int u) {
	if(Fa[u]==u) return u;
	return Fa[u]=find(Fa[u]);
}

void dfs2(int u) {
	for(auto& v:vec[u]) {
		if(find(u)!=find(v)) {siz[find(u)]-=siz[find(v)];}
		dfs2(v);
	}
}

int ans;
signed main() {
	cin >> n >> m;k=(1ll<<n);
	
	int o,u;
	for(int i=1;i<=m;++i) {
		cin >> o >> u;
		op[i]=o;int num=u,j;
		for(j=n;num<(1ll<<n-1);num*=2,--j);
		qst[i]=nodes[i]={num,j};
	}
	sort(nodes+1,nodes+1+m);
	l=unique(nodes+1,nodes+1+m)-nodes-1;
	
	dfs(1,1);
	vec[l+1].push_back(1);siz[l+1]=k-1,Fa[1]=fa[1]=l+1,Fa[l+1]=l+1;
	int p;
	for(int i=1;i<=m;++i) {
		if(op[i]==2) continue;
		p=lower_bound(nodes+1,nodes+1+l,qst[i])-nodes;Fa[p]=p;cnt[p]++;
	}
	dfs2(l+1);
	for(int i=m;i>=1;--i) {
		p=lower_bound(nodes+1,nodes+1+l,qst[i])-nodes;
		if(op[i]==1) {
			cnt[p]--;
			if(cnt[p]==0) siz[find(fa[p])]+=siz[find(p)],Fa[find(p)]=find(fa[p]);
		}else {
			ans^=siz[find(p)];
		}
	}
	
	cout << ans;
	
	return 0;
}