Problem p02599 (C++) — buggy submission, verdict: Runtime Error

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace std;
using namespace __gnu_pbds;
typedef tree<int, null_type, less<int>, rb_tree_tag,
             tree_order_statistics_node_update>
    pbds;

int main() {
  // que[R] = {L, index_of_query};
  // um is map such that um[element] = last index the element was seen
  // s - a set that contains the last index as mentioned above
  // code assumes 0 indexed
  // complexity - O(n*log(n))
  unordered_map<int, int> um;
  pbds s;
  int n, q;
  cin >> n >> q;
  vector<int> a(n + 1);
  for (int i = 1; i <= n; i++)
    cin >> a[i];
  // q; //cin >> q;
  vector<int> ans(q + 1);
  vector<vector<pair<int, int>>> que(n + 1);
  for (int i = 1; i <= q; i++) {
    int L, R;
    cin >> L >> R;
    que[R].push_back({L, i});
  }
  for (int i = 1; i <= n; i++) {
    if (um.count(a[i]))
      s.erase(um[a[i]]);
    um[a[i]] = i;
    s.insert(i);
    for (auto it : que[i])
      ans[it.second] = s.size() - s.order_of_key(it.first);
  }
  for (int i = 1; i <= q; i++)
    cout << ans[i] << "\\n";
  return 0;
}

Error: -11

Fixed submission:

#include <bits/stdc++.h>

#define DB(x) cout << #x << "=" << x << endl;

using namespace std;

const int MAXN = 6 * (1e5);

const long MAXS = 2e7;
vector<long> root(MAXN), root2(MAXN);

// Begin persistent segment tree
long lch[MAXS], rch[MAXS], sum2[MAXS], cnt;

long new_node(int val) {
  assert(cnt < MAXS);
  sum2[cnt] = val;
  return cnt++;
}

int new_node(int l, int r, bool s) {
  lch[cnt] = l;
  rch[cnt] = r;

  return new_node(s ? sum2[l] + sum2[r] : max(sum2[l], sum2[r]));
}

int build(int b, int e) {
  if (b == e)
    return new_node(0);

  int m = (b + e) / 2;
  return new_node(build(b, m), build(m + 1, e), false);
}

int update2(int v, int b, int e, int p, int val, bool s) {
  if (b > p || e < p)
    return v;

  if (b == e)
    return new_node(val);

  int m = (b + e) / 2;
  int l = update2(lch[v], b, m, p, val, s),
      r = update2(rch[v], m + 1, e, p, val, s);

  return new_node(l, r, s);
}

int query(int v, int b, int e, int l, int r, bool s) {
  if (e < l || b > r)
    return 0;

  if (l <= b && e <= r)
    return sum2[v];

  int m = (b + e) / 2;

  if (s)
    return query(lch[v], b, m, l, r, s) + query(rch[v], m + 1, e, l, r, s);
  else
    return max(query(lch[v], b, m, l, r, s), query(rch[v], m + 1, e, l, r, s));
}

// End persistent segment tree

long long n, a[MAXN], next_pos[MAXN], forw[MAXN], q, l, r;

vector<long> pos(MAXN), last(MAXN);

void update(int r, int a, int b) {
  root2[a] = update2(r, 0, MAXN - 1, a, b, 0);
}

int dquery(int l, int r) {
  return query(root[r + 1], 0, MAXN - 1, l + 1, r + 1, 1);
}

int main() {
  int aisehi;
  cin.sync_with_stdio(false);
  cin.tie(0);

  cin >> n >> q;

  for (int i = 0; i < n; ++i)
    cin >> a[i];

  root[0] = build(0, MAXN - 1);
  root2[n] = build(0, MAXN - 1);

  for (int i = 1; i <= n; ++i) {
    int r = root[i - 1];
    int a = ::a[i - 1];

    if (pos[a])
      r = update2(r, 0, MAXN - 1, pos[a], 0, 1);

    root[i] = update2(r, 0, MAXN - 1, i, 1, 1);
    pos[a] = i;
  }

  memset(forw, -1, sizeof forw);

  for (int i = n - 1; i >= 0; --i) {
    if (forw[a[i]] == -1) {
      update(root2[i + 1], i, MAXN - 2);
      next_pos[i] = MAXN - 2;
      last[i] = MAXN - 2;
    } else {
      int idx = forw[a[i]];
      int rot = update2(root2[i + 1], 0, MAXN - 1, idx, 0, 0);
      int r = next_pos[idx];
      next_pos[i] = idx;

      if (r == MAXN - 2 || r - idx != idx - i) {
        update(rot, i, r);
        last[i] = r;
      } else {
        update(rot, i, last[idx]);
        last[i] = last[idx];
      }
    }

    forw[a[i]] = i;
  }

  // cin >> q;

  for (int i = 0; i < q; ++i) {
    cin >> l >> r;
    --l, --r;
    int ans = dquery(l, r);
    int cnt = query(root2[l], 0, MAXN - 1, l, r, 0);
    ans += cnt <= r;
    cout << ans << '\\n';
  }
  return 0;
}