merge_sort_tree.cpp

// Problem : https://codeforces.com/problemset/problem/893/F
// About this code : MergeSort Tree without updates, precomputed prefix minimums
// for all segtree[u] vectors to query min( second value in pair, which is
// sorted by first value)

/**
 *	Author: Nachiket Kanore
 *	Created: Wednesday 07 April 2021 06:08:57 PM IST
 **/
#include <algorithm>
#include <array>
#include <cassert>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <string>
#include <vector>

#define pb push_back
#define sz(x) (int)(x.size())
#define ALL(x) (x).begin(), (x).end()
#define F0R(i, R) for (int i = (0); i < (R); ++i)
#define FOR(i, L, R) for (int i = (L); i <= (R); ++i)
using namespace std;

template <typename T> ostream &operator<<(ostream &os, const vector<T> &v) {
  os << '{';
  string sep;
  for (const auto &x : v)
    os << sep << x, sep = ", ";
  return os << '}';
}
template <typename T, size_t size>
ostream &operator<<(ostream &os, const array<T, size> &arr) {
  os << '{';
  string sep;
  for (const auto &x : arr)
    os << sep << x, sep = ", ";
  return os << '}';
}
template <typename A, typename B>
ostream &operator<<(ostream &os, const pair<A, B> &p) {
  return os << '(' << p.first << ", " << p.second << ')';
}

void dbg_out() { cerr << endl; }
template <typename Head, typename... Tail> void dbg_out(Head H, Tail... T) {
  cerr << ' ' << H;
  dbg_out(T...);
}

#ifdef DEBUG
#define see(...) cerr << "(" << #__VA_ARGS__ << "):", dbg_out(__VA_ARGS__)
#else
#define see(...)
#endif

template <class T> bool cmin(T &a, const T &b) { return b < a ? a = b, 1 : 0; }
template <class T> bool cmax(T &a, const T &b) { return a < b ? a = b, 1 : 0; }

const int inf = 2e9;
const int N = 1e5 + 5;

int root, n, a[N], depth[N], val[N], tin[N], tout[N], timer;
pair<int, int> keep[N];
vector<int> g[N];

struct MergeSortTree {
  vector<pair<int, int>> tree[N << 2];
  vector<int> prefix_minimums[N << 2];

  void merge(int u) {
    int x = 2 * u, y = 2 * u + 1;
    assert(is_sorted(ALL(tree[x])) && is_sorted(ALL(tree[y])));
    int i = 0, j = 0;
    while (i < sz(tree[x]) || j < sz(tree[y])) {
      if (i == sz(tree[x])) {
        tree[u].push_back(tree[y][j++]);
      } else if (j == sz(tree[y])) {
        tree[u].push_back(tree[x][i++]);
      } else {
        if (tree[x][i] < tree[y][j]) {
          tree[u].push_back(tree[x][i++]);
        } else {
          tree[u].push_back(tree[y][j++]);
        }
      }
    }
  }

  void init() {
    build(1, 1, n);
    F0R(i, N << 2) {
      int mn = inf;
      for (auto [h, v] : tree[i]) {
        cmin(mn, v);
        prefix_minimums[i].push_back(mn);
      }
    }
  }

  void build(int u, int tl, int tr) {
    if (tl == tr) {
      tree[u].emplace_back(keep[tl]);
    } else {
      int mid = (tl + tr) >> 1;
      build(2 * u, tl, mid);
      build(2 * u + 1, mid + 1, tr);
      merge(u);
    }
  }

  int qry(int u, int tl, int tr, int ql, int qr, int max_depth) {
    if (tl > tr || ql > qr || qr < tl || ql > tr)
      return inf;
    if (tl == ql && tr == qr) {
      int ret = inf;
      int id = -1, lo = 0, hi = sz(tree[u]) - 1;
      while (lo <= hi) {
        int mid = (lo + hi) >> 1;
        if (tree[u][mid].first <= max_depth) {
          id = mid;
          lo = mid + 1;
        } else {
          hi = mid - 1;
        }
      }
      if (~id)
        ret = prefix_minimums[u][id];
      return ret;
    }
    int mid = (tl + tr) >> 1;
    return min(qry(2 * u, tl, mid, ql, min(mid, qr), max_depth),
               qry(2 * u + 1, mid + 1, tr, max(mid + 1, ql), qr, max_depth));
  }

  int query(int L, int R, int max_depth) {
    return qry(1, 1, n, L, R, max_depth);
  }
} T;

void dfs(int u, int par, int dep) {
  depth[u] = dep;
  tin[u] = ++timer;
  keep[timer] = make_pair(depth[u], val[u]);
  for (int v : g[u])
    if (v ^ par)
      dfs(v, u, dep + 1);
  tout[u] = timer;
}

int32_t main() {
  ios::sync_with_stdio(0);
  cin.tie(0);

  cin >> n >> root;
  FOR(i, 1, n) cin >> val[i];
  FOR(i, 2, n) {
    int u, v;
    cin >> u >> v;
    g[u].push_back(v);
    g[v].push_back(u);
  }
  dfs(root, root, 0);
  T.init();
  int Q, last = 0;
  cin >> Q;
  while (Q--) {
    int u, dist;
    cin >> u >> dist;
    u = (u + last) % n + 1;
    dist = (dist + last) % n;
    dist += depth[u];
    last = T.query(tin[u], tout[u], dist);
    cout << last << '\n';
  }
}