SXCPC2018 nucoj2004 国王的怪癖

可持久化trie。考场上我脑补了一个trie树合并也A了

#include <iostream>
#include <cstring>
#include <cstdio>
using namespace std;
int n, k, m, dfnl[100005], dfnr[100005], idx, rot[100005], v[100005], uu, vv, cnt;
int hea[100005], fan[100005], tot;
struct Edge{
	int too, nxt, val;
}edge[200005];
struct Node{
	int l, r, sum;
}nd[3333333];
void add_edge(int fro, int too){
	edge[++cnt].nxt = hea[fro];
	edge[cnt].too = too;
	hea[fro] = cnt;
}
void dfs(int x, int f){
	dfnl[x] = ++idx;
	fan[idx] = x;
	for(int i=hea[x]; i; i=edge[i].nxt){
		int t=edge[i].too;
		if(t!=f)	dfs(t, x);
	}
	dfnr[x] = idx;
}
int update(int pre, int x, int p){
	int re=++tot;
	nd[re] = nd[pre];
	nd[re].sum++;
	if(p<0)
		return re;
	int tmp=(x>>p)&1;
	if(tmp)	nd[re].r = update(nd[pre].r, x, p-1);
	else	nd[re].l = update(nd[pre].l, x, p-1);
	return re;
}
int query(int pre, int now, int x, int p){
	if(p<0)	return 0;
	int tmp=(x>>p)&1;
	if(tmp){
		int sum=nd[nd[now].l].sum-nd[nd[pre].l].sum;
		if(sum)
			return query(nd[pre].l, nd[now].l, x, p-1)+(1<<p);
		else
			return query(nd[pre].r, nd[now].r, x, p-1);
	}
	else{
		int sum=nd[nd[now].r].sum-nd[nd[pre].r].sum;
		if(sum)
			return query(nd[pre].r, nd[now].r, x, p-1)+(1<<p);
		else
			return query(nd[pre].l, nd[now].l, x, p-1);
	}
}
int main(){
	while(scanf("%d %d %d", &n, &k, &m)!=EOF){
		memset(hea, 0, sizeof(hea));
		idx = tot = cnt = 0;
		for(int i=1; i<=n; i++)
			scanf("%d", &v[i]);
		for(int i=1; i<n; i++){
			scanf("%d %d", &uu, &vv);
			add_edge(uu, vv);
			add_edge(vv, uu);
		}
		dfs(k, 0);
		for(int i=1; i<=n; i++)
			rot[i] = update(rot[i-1], v[fan[i]], 30);
		while(m--){
			scanf("%d %d", &uu, &vv);
			printf("%d\n", query(rot[dfnl[uu]-1], rot[dfnr[uu]], vv, 30));
		}
	}
	return 0;
}