「vijos-bashu」lxhgww的奇思妙想(长链剖分)

倍增离线，预处理出爹和孙子们。查询\(O(1)\)

#include <cstdio>
#include <cstring>
#include <numeric>
#include <cmath>
#include <algorithm>
#include <iostream>
#define R(a,b,c) for(register int a = (b); a <= (c); ++a)
#define nR(a,b,c) for(register int a = (b); a >= (c); --a)
#define Swap(a,b) ((a) ^= (b) ^= (a) ^= (b))
#define MP make_pair
#ifdef QWQ
#define FileOpen() freopen("in.txt", "r", stdin)
#define FileSave() freopen("out.txt", "w", stdout)
#define D_e_Line cerr << "\n--------\n"
#define D_e(x) cerr << (#x) << " : " << x << endl
#define C_e(x) cout << (#x) << " : " << x << endl
#define Pause() system("pause")
#define TIME() fprint(stderr, "TIME : %.3lfms\n", (double)clock() / (double)CLOCKS_PER_SEC)
#include <cassert>
#else
#define FileOpen()
#define FileSave()
#define D_e_Line
#define D_e(x)
#define C_e(x)
#define Pause()
#define TIME()
#endif
struct FastIO {
	template<typename ATP> inline FastIO & operator >> (ATP & x)  {
		x = 0; int f = 1; char c;
		for(c = getchar(); c < '0' || c > '9'; c = getchar()) if(c == '-') f = -1;
		while(c >= '0' && c <= '9') x = x * 10 + (c ^ '0'), c = getchar();
		if(f == -1) x = -x;
		return *this;
	}
} io;
using namespace std;
template<typename ATP> inline ATP Max(ATP x, ATP y) {
	return x > y ? x : y;
}
template<typename ATP> inline ATP Min(ATP x, ATP y) {
	return x < y ? x : y;
}
template<typename ATP> inline ATP Abs(ATP x) {
	return x > 0 ? x : -x;
}
#include <vector>
const int N = 3e5 + 7;
vector<int> D[N], U[N];
struct Edge {
	int nxt, pre;
} e[N << 1];
int head[N], cntEdge;
inline void add(int u, int v) {
	e[++cntEdge] = (Edge){ head[u], v}, head[u] = cntEdge;
}
int n;
int f[N][21], dep[N], md[N], len[N], son[N], top[N];
inline void DFS_First(int u, int father) {
	f[u][0] = father, md[u] = dep[u] = dep[father] + 1;
	R(i,1,19){
		if(f[u][i - 1]) f[u][i] = f[f[u][i - 1]][i - 1];
		else break;
	}
	for(register int i = head[u]; i; i = e[i].nxt){
		int v = e[i].pre;
		if(v == father) continue;
		DFS_First(v, u);
		if(md[v] > md[son[u]]) son[u] = v, md[u] = md[v];
	}
}
void DFS_Second(int u, int Tp) {
	top[u] = Tp, len[u] = md[u] - dep[Tp] + 1;
	if(!son[u]) return;
	DFS_Second(son[u], Tp);
	for(register int i = head[u]; i; i = e[i].nxt){
		int v = e[i].pre;
		if(v != f[u][0] && v != son[u])
			DFS_Second(v, v);
	}
}
int H[N];
inline void Init() {
	int now = 0;
	R(i,1,n){
		if(!(i & (1 << now))) ++now;
		H[i] = now;
	}
	R(i,1,n){
		if(i == top[i]){
			for(register int j = 1, u = i; j <= len[i] && u; ++j) u = f[u][0], U[i].push_back(u);
			for(register int j = 1, u = i; j <= len[i] && u; ++j) u = son[u], D[i].push_back(u);
		}
	}
}
inline int Query(int u, int K) {
	if(K > dep[u]) return 0;
	if(!K) return u;
	u = f[u][H[K]], K ^= (1 << H[K]);
	if(!K) return u;
	if(dep[u] - dep[top[u]] == K) return top[u];
	if(dep[u] - dep[top[u]] < K) return U[top[u]][K - dep[u] + dep[top[u]] - 1];
	return D[top[u]][dep[u] - dep[top[u]] - K - 1];
}
int main() {
	io >> n;
	R(i,2,n){
		int u, v;
		io >> u >> v;
		add(u, v);
		add(v, u);
	}
	DFS_First(1, 0);
	DFS_Second(1, 1);
	Init();
	int lst = 0, Q;
	io >> Q;
	while(Q--){
		int u, K;
		io >> u >> K;
		u ^= lst, K ^= lst;
		printf("%d\n", lst = Query(u, K));
	}
	return 0;
}