Problem p02599 (C++)

Buggy submission (status: 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 __gnu_pbds;

#define ff first
#define ss second
#define ll int64_t
#define ld long double
#define nl cout << "\n"
#define all(v) v.begin(), v.end()
#define mset(a, v) memset((a), (v), sizeof(a))
#define forn(i, a, b) for (int64_t i = int64_t(a); i < int64_t(b); ++i)
#define forb(i, a, b) for (int64_t i = int64_t(a); i >= int64_t(b); --i)
#define fastio()                                                               \
  ios::sync_with_stdio(false);                                                 \
  cin.tie(0);                                                                  \
  cout.tie(0);
#define ordered_set                                                            \
  tree<int, null_type, less<int>, rb_tree_tag,                                 \
       tree_order_statistics_node_update>

#define mod 1000000007
#define mod2 998244353
#define inf 1000000000000007
#define pi 3.14159265358979323846

template <class L, class R> ostream &operator<<(ostream &out, pair<L, R> &p) {
  return out << "(" << p.ff << ", " << p.ss << ")";
}
template <class T> ostream &operator<<(ostream &out, vector<T> &v) {
  out << "[";
  for (auto it = v.begin(); it != v.end(); ++it) {
    if (it != v.begin())
      out << ", ";
    out << *it;
  }
  return out << "]";
}
template <class T> ostream &operator<<(ostream &out, deque<T> &v) {
  out << "[";
  for (auto it = v.begin(); it != v.end(); ++it) {
    if (it != v.begin())
      out << ", ";
    out << *it;
  }
  return out << "]";
}
template <class T> ostream &operator<<(ostream &out, set<T> &s) {
  out << "{";
  for (auto it = s.begin(); it != s.end(); ++it) {
    if (it != s.begin())
      out << ", ";
    out << *it;
  }
  return out << "}";
}
template <class L, class R> ostream &operator<<(ostream &out, map<L, R> &m) {
  out << "{";
  for (auto it = m.begin(); it != m.end(); ++it) {
    if (it != m.begin())
      out << ", ";
    out << *it;
  }
  return out << "}";
}

void dbg_out() { cerr << "]\n"; }
template <typename Head, typename... Tail> void dbg_out(Head H, Tail... T) {
  cerr << H;
  if (sizeof...(Tail))
    cerr << ", ";
  dbg_out(T...);
}
#ifdef LOCAL
#define dbg(...) cerr << "[" << #__VA_ARGS__ << "] = [", dbg_out(__VA_ARGS__)
#else
#define dbg(...)
#endif

ll count_digits(ll n) {
  ll dig = floor(log10(n) + 1);
  return dig;
}
ll mpow(ll x, ll y, ll p) {
  ll r = 1;
  x = x % p;
  while (y > 0) {
    if (y & 1)
      r = (r * x) % p;
    y = y >> 1;
    x = (x * x) % p;
  }
  return r;
}
ll mod_inv(ll a, ll m) {
  ll m0 = m, y = 0, x = 1;
  if (m == 1)
    return 0;
  while (a > 1) {
    ll q = a / m, t = m;
    m = a % m, a = t;
    t = y;
    y = x - q * y;
    x = t;
  }
  if (x < 0)
    x += m0;
  return x;
}
/* const ll MAXN=1000007;ll spf[MAXN+5];vector<ll> prime; */
/* void sieve(ll n)        {forn(i,2,MAXN+1)spf[i]=i;for(ll
 * i=2;i*i<=n;i++)if(spf[i]==i)for(ll
 * j=i*i;j<=n;j+=i)if(spf[j]==j)spf[j]=i;forn(i,2,MAXN+1)if(spf[i]==i)prime.push_back(i);}
 */

//-------------------------------L_I_Erq34-------------------------------

vector<ll> a, b;
vector<vector<ll>> segtree;

void build(ll n) {
  forn(i, 0, n) segtree[i + n] = {a[i]};
  forb(i, n - 1, 0) {
    segtree[i].resize(segtree[i << 1].size() + segtree[i << 1 | 1].size());
    merge(all(segtree[i << 1]), all(segtree[i << 1 | 1]), segtree[i].begin());
  }
}

ll query(ll n, ll l, ll r) {
  ll res = 0, val = r - 1;
  for (l += n, r += n; l < r; l >>= 1, r >>= 1) {
    if (l & 1) {
      res += segtree[l].end() - upper_bound(all(segtree[l]), val);
      l++;
    }
    if (r & 1) {
      r--;
      res += segtree[r].end() - upper_bound(all(segtree[r]), val);
    }
  }
  return res;
}

int main() {
  fastio();
  ll z, n, m, t, k, i, j, l, d, h, r;
  cin >> n >> m;
  a = b = vector<ll>(n, inf);
  for (ll &i : a) {
    cin >> i;
    i--;
  }
  forb(i, n - 1, 0) {
    r = b[a[i]];
    b[a[i]] = i;
    a[i] = r;
  }
  segtree = vector<vector<ll>>(n << 1);
  build(n);
  while (m--) {
    cin >> l >> r;
    cout << query(n, l - 1, r) << "\n";
  }
  cerr << "\nTime elapsed: " << 1000 * clock() / CLOCKS_PER_SEC << "ms\n";
  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace std;
using namespace __gnu_pbds;

#define ff first
#define ss second
#define ll int64_t
#define ld long double
#define nl cout << "\n"
#define all(v) v.begin(), v.end()
#define mset(a, v) memset((a), (v), sizeof(a))
#define forn(i, a, b) for (int64_t i = int64_t(a); i < int64_t(b); ++i)
#define forb(i, a, b) for (int64_t i = int64_t(a); i >= int64_t(b); --i)
#define fastio()                                                               \
  ios::sync_with_stdio(false);                                                 \
  cin.tie(0);                                                                  \
  cout.tie(0);
#define ordered_set                                                            \
  tree<int, null_type, less<int>, rb_tree_tag,                                 \
       tree_order_statistics_node_update>

#define mod 1000000007
#define mod2 998244353
#define inf 1000000000000007
#define pi 3.14159265358979323846

template <class L, class R> ostream &operator<<(ostream &out, pair<L, R> &p) {
  return out << "(" << p.ff << ", " << p.ss << ")";
}
template <class T> ostream &operator<<(ostream &out, vector<T> &v) {
  out << "[";
  for (auto it = v.begin(); it != v.end(); ++it) {
    if (it != v.begin())
      out << ", ";
    out << *it;
  }
  return out << "]";
}
template <class T> ostream &operator<<(ostream &out, deque<T> &v) {
  out << "[";
  for (auto it = v.begin(); it != v.end(); ++it) {
    if (it != v.begin())
      out << ", ";
    out << *it;
  }
  return out << "]";
}
template <class T> ostream &operator<<(ostream &out, set<T> &s) {
  out << "{";
  for (auto it = s.begin(); it != s.end(); ++it) {
    if (it != s.begin())
      out << ", ";
    out << *it;
  }
  return out << "}";
}
template <class L, class R> ostream &operator<<(ostream &out, map<L, R> &m) {
  out << "{";
  for (auto it = m.begin(); it != m.end(); ++it) {
    if (it != m.begin())
      out << ", ";
    out << *it;
  }
  return out << "}";
}

void dbg_out() { cerr << "]\n"; }
template <typename Head, typename... Tail> void dbg_out(Head H, Tail... T) {
  cerr << H;
  if (sizeof...(Tail))
    cerr << ", ";
  dbg_out(T...);
}
#ifdef LOCAL
#define dbg(...) cerr << "[" << #__VA_ARGS__ << "] = [", dbg_out(__VA_ARGS__)
#else
#define dbg(...)
#endif

ll count_digits(ll n) {
  ll dig = floor(log10(n) + 1);
  return dig;
}
ll mpow(ll x, ll y, ll p) {
  ll r = 1;
  x = x % p;
  while (y > 0) {
    if (y & 1)
      r = (r * x) % p;
    y = y >> 1;
    x = (x * x) % p;
  }
  return r;
}
ll mod_inv(ll a, ll m) {
  ll m0 = m, y = 0, x = 1;
  if (m == 1)
    return 0;
  while (a > 1) {
    ll q = a / m, t = m;
    m = a % m, a = t;
    t = y;
    y = x - q * y;
    x = t;
  }
  if (x < 0)
    x += m0;
  return x;
}
/* const ll MAXN=1000007;ll spf[MAXN+5];vector<ll> prime; */
/* void sieve(ll n)        {forn(i,2,MAXN+1)spf[i]=i;for(ll
 * i=2;i*i<=n;i++)if(spf[i]==i)for(ll
 * j=i*i;j<=n;j+=i)if(spf[j]==j)spf[j]=i;forn(i,2,MAXN+1)if(spf[i]==i)prime.push_back(i);}
 */

//-------------------------------L_I_Erq34-------------------------------

vector<ll> a, b;
vector<vector<ll>> segtree;

void build(ll n) {
  forn(i, 0, n) segtree[i + n] = {a[i]};
  forb(i, n - 1, 1) {
    segtree[i].resize(segtree[i << 1].size() + segtree[i << 1 | 1].size());
    merge(all(segtree[i << 1]), all(segtree[i << 1 | 1]), segtree[i].begin());
  }
}

ll query(ll n, ll l, ll r) {
  ll res = 0, val = r - 1;
  for (l += n, r += n; l < r; l >>= 1, r >>= 1) {
    if (l & 1) {
      res += segtree[l].end() - upper_bound(all(segtree[l]), val);
      l++;
    }
    if (r & 1) {
      r--;
      res += segtree[r].end() - upper_bound(all(segtree[r]), val);
    }
  }
  return res;
}

int main() {
  fastio();
  ll z, n, m, t, k, i, j, l, d, h, r;
  cin >> n >> m;
  a = b = vector<ll>(n, inf);
  for (ll &i : a) {
    cin >> i;
    i--;
  }
  forb(i, n - 1, 0) {
    r = b[a[i]];
    b[a[i]] = i;
    a[i] = r;
  }
  segtree = vector<vector<ll>>(n << 1);
  build(n);
  while (m--) {
    cin >> l >> r;
    cout << query(n, l - 1, r) << "\n";
  }
  cerr << "\nTime elapsed: " << 1000 * clock() / CLOCKS_PER_SEC << "ms\n";
  return 0;
}