[vijos]lxhgww的奇思妙想(长链剖分)

#include<bits/stdc++.h>
using namespace std;
const int MAXN = 3e5 + 10;
inline int read() {
    char c = getchar(); int x = 0, f = 1;
    while(c < '0' || c > '9') {if(c == '-') f = -1; c = getchar();}
    while(c >= '0' && c <= '9') x = x * 10 + c - '0', c = getchar();
    return x * f;
}
int N, md[MAXN], dep[MAXN], fa[MAXN][21], son[MAXN], top[MAXN], len[MAXN], B[MAXN];
vector<int> v[MAXN], U[MAXN], D[MAXN];//up and down
void dfs(int x, int _fa) {
    md[x] = dep[x] = dep[_fa] + 1;  fa[x][0] = _fa;
    for(int i = 1; i < 20; i++) 
        if(fa[x][i - 1]) fa[x][i] = fa[fa[x][i - 1]][i - 1];
        else break;
    for(int i = 0, to; i < v[x].size(); i++) {
        if((to = v[x][i]) == _fa) continue;
        dfs(to, x); 
        if(md[to] > md[son[x]]) son[x] = to, md[x] = md[to];
    }
} 
void dfs2(int x, int topf) {
    top[x] = topf; len[x] = md[x] - dep[topf] + 1;
    if(!son[x]) return ;
    dfs2(son[x], topf);
    for(int i = 0, to; i < v[x].size(); i++) 
        if(!top[(to = v[x][i])]) dfs2(to, to);
}
void Pre() {
    int now = 0;
    for(int i = 1; i <= N; i++) {
        if(!(i & (1 << now))) now++;
        B[i] = now;
    }
    for(int i = 1; i <= N; i++) {
        if(i == top[i]) {
            for(int j = 1, x = i; j <= len[i] && x; j++) x = fa[x][0], U[i].push_back(x);
            for(int j = 1, x = i; j <= len[i] && x; j++) x = son[x], D[i].push_back(x); 
        }
    }
}
int Query(int x, int k) {
    if(k > dep[x]) return 0;
    if(k == 0) return x;
    x = fa[x][B[k]]; k ^= 1 << B[k]; 
    if(!k) return x;
    if(dep[x] - dep[top[x]] == k) return top[x];
    if(dep[x] - dep[top[x]] < k) return U[top[x]][k - dep[x] + dep[top[x]] - 1];
    else return D[top[x]][dep[x] - dep[top[x]] - k - 1];
}
int main() {
    N = read();
    for(int i = 1; i <= N - 1; i++) {
        int x = read(), y = read();
        v[x].push_back(y); v[y].push_back(x);
    }
    dfs(1, 0); dfs2(1, 1);
    Pre();
    int lastans = 0, Q = read();
    while(Q--) {
        int x = read() ^ lastans, y = read() ^ lastans;
        printf("%d\n", lastans = Query(x, y));
    }
    return 0;
}