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

#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;

template <class Abel> struct BIT {
  vector<Abel> dat[2];
  Abel UNITY_SUM = 0; // to be set

  /* [1, n] */
  BIT(int n) { init(n); }
  void init(int n) {
    for (int iter = 0; iter < 2; ++iter)
      dat[iter].assign(n + 1, UNITY_SUM);
  }

  /* a, b are 1-indexed, [a, b) */
  inline void sub_add(int p, int a, Abel x) {
    for (int i = a; i < (int)dat[p].size(); i += i & -i)
      dat[p][i] = dat[p][i] + x;
  }
  inline void add(int a, int b, Abel x) {
    sub_add(0, a, x * -(a - 1));
    sub_add(1, a, x);
    sub_add(0, b, x * (b - 1));
    sub_add(1, b, x * (-1));
  }

  /* a is 1-indexed, [a, b) */
  inline Abel sub_sum(int p, int a) {
    Abel res = UNITY_SUM;
    for (int i = a; i > 0; i -= i & -i)
      res = res + dat[p][i];
    return res;
  }
  inline Abel sum(int a, int b) {
    return sub_sum(0, b - 1) + sub_sum(1, b - 1) * (b - 1) - sub_sum(0, a - 1) -
           sub_sum(1, a - 1) * (a - 1);
  }

  /* debug */
  void print() {
    for (int i = 1; i < (int)dat[0].size(); ++i)
      cout << sum(i, i + 1) << ",";
    cout << endl;
  }
};

int main() {
  int N;
  cin >> N;
  int Q;
  cin >> Q;
  vector<int> a(N);
  for (int i = 0; i < N; ++i)
    cin >> a[i];

  vector<int> lefts(Q), rights(Q), ids(Q);
  for (int i = 0; i < Q; ++i) {
    cin >> lefts[i] >> rights[i];
    --lefts[i];
    ids[i] = i;
  }
  sort(ids.begin(), ids.end(),
       [&](int i, int j) { return rights[i] < rights[j]; });

  BIT<int> bit(N + 5);
  vector<int> prev(1100000, -1);
  vector<int> res(Q, 0);
  int r = 0;
  for (auto i : ids) {
    for (; r < rights[i]; ++r) {
      bit.add(prev[a[r]] + 2, r + 2, 1);
      prev[a[r]] = r;
    }
    int tmp = bit.sum(lefts[i] + 1, lefts[i] + 2);
    res[i] = max(res[i], tmp);
  }
  for (int i = 0; i < Q; ++i)
    cout << res[i] << endl;
}

Error: WA

Fixed submission:

#include <bits/stdc++.h>
// #include <boost/multiprecision/cpp_int.hpp>
using namespace std;

using dou = long double;
string yes = "yes";
string Yes = "Yes";
string YES = "YES";
string no = "no";
string No = "No";
string NO = "NO";

template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
typedef long long ll;
typedef pair<int, int> P;
typedef pair<ll, ll> PL;
const ll mod = 1000000007ll;
// const ll mod = 10007;

struct mint {
  ll x; // typedef long long ll;
  mint(ll x = 0) : x((x % mod + mod) % mod) {}
  mint operator-() const { return mint(-x); }
  mint &operator+=(const mint a) {
    if ((x += a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator-=(const mint a) {
    if ((x += mod - a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator*=(const mint a) {
    (x *= a.x) %= mod;
    return *this;
  }
  mint operator+(const mint a) const { return mint(*this) += a; }
  mint operator-(const mint a) const { return mint(*this) -= a; }
  mint operator*(const mint a) const { return mint(*this) *= a; }
  mint pow(ll t) const {
    if (!t)
      return 1;
    mint a = pow(t >> 1);
    a *= a;
    if (t & 1)
      a *= *this;
    return a;
  }

  // for prime mod
  mint inv() const { return pow(mod - 2); }
  mint &operator/=(const mint a) { return *this *= a.inv(); }
  mint operator/(const mint a) const { return mint(*this) /= a; }
};
istream &operator>>(istream &is, const mint &a) { return is >> a.x; }
ostream &operator<<(ostream &os, const mint &a) { return os << a.x; }

#define rep(i, n) for (ll i = 0; i < (ll)(n); i++)
#define brep(n) for (int bit = 0; bit < (1 << n); bit++)
#define bbrep(n) for (int bbit = 0; bbit < (1 << n); bbit++)
#define erep(i, container) for (auto &i : container)
#define itrep(i, container) for (auto i : container)
#define irep(i, n) for (ll i = n - 1; i >= (ll)0ll; i--)
#define rrep(i, m, n) for (ll i = m; i < (ll)(n); i++)
#define reprep(i, j, h, w) rep(i, h) rep(j, w)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define VEC(type, name, n)                                                     \\
  std::vector<type> name(n);                                                   \\
  rep(i, n) std::cin >> name[i];
#define pb push_back
#define pf push_front
#define query                                                                  \\
  int qq;                                                                      \\
  std::cin >> qq;                                                              \\
  rep(qqq, qq)
#define lb lower_bound
#define ub upper_bound
#define fi first
#define se second
#define itn int
#define mp make_pair
#define sum(a) accumulate(all(a), 0ll)
#define keta fixed << setprecision
#define vout(a)                                                                \\
  erep(qxqxqx, a) std::cout << qxqxqx << ' ';                                  \\
  std::cout << std::endl;
#define vvector(name, typ, m, n, a)                                            \\
  vector<vector<typ>> name(m, vector<typ>(n, a))
// #define vvector(name,typ,m,n)vector<vector<typ> > name(m,vector<typ> (n))
#define vvvector(name, t, l, m, n, a)                                          \\
  vector<vector<vector<t>>> name(l, vector<vector<t>>(m, vector<t>(n, a)));
#define vvvvector(name, t, k, l, m, n, a)                                      \\
  vector<vector<vector<vector<t>>>> name(                                      \\
      k, vector<vector<vector<t>>>(l, vector<vector<t>>(m, vector<t>(n, a))));
#define case std::cout << "Case #" << qqq + 1 << ":"
#define res resize
#define as assign
#define ffor for (;;)
#define ppri(a, b) std::cout << a << " " << b << std::endl
#define pppri(a, b, c) std::cout << a << " " << b << " " << c << std::endl
#define aall(x, n) (x).begin(), (x).begin() + (n)
#define ssum(a) accumulate(a, 0ll)
#define stirng string
#define gin(a, b)                                                              \\
  int a, b;                                                                    \\
  std::cin >> a >> b;                                                          \\
  a--;                                                                         \\
  b--;
// #define grid_input(a,type) int h,w;std::cin >>
// h>>w;vvector(a,type,h,w,0);reprep(i,j,h,w)std::cin >> a[i][j];

// typedef long long T;
ll ceil(ll a, ll b) { return ((a + b - 1) / b); }
const int INF = 2000000000;
// const ll INF64 =3223372036854775807ll;
// const ll INF64 = 9223372036854775807ll;
const ll INF64 = 9223372036854775ll;
const ll MOD = 1000000007ll;
// const ll MOD = 1000003ll;
const ll OD = 1000000000000007ll;
const dou pi = 3.141592653589793;
long long modpow(long long a, long long n) { // 累乗の余剰
  long long res = 1;
  while (n > 0) {
    if (n & 1)
      res = res * a % MOD;
    a = a * a % MOD;
    n >>= 1;
  }
  return res;
}

// メモ
// tuple<hoge,huga,foo> tのget関数はget<i>(t)
// resizeはメンバ関数
// 三項演算子を覚えよう
//  a?b:cと書くと aならばbの処理をする
struct Mo {
  vector<int> left, right, order;
  vector<bool> v;
  int width;
  int nl, nr, ptr;

  Mo(int n) : width((int)sqrt(n)), nl(0), nr(0), ptr(0), v(n) {}

  void insert(int l, int r) /* [l, r) */
  {
    left.push_back(l);
    right.push_back(r);
  }

  /* ソート */
  void build() {
    order.resize(left.size());
    iota(begin(order), end(order), 0);
    sort(begin(order), end(order), [&](int a, int b) {
      if (left[a] / width != left[b] / width)
        return left[a] < left[b];
      return right[a] < right[b];
    });
  }

  /* クエリを 1 つぶんすすめて, クエリのidを返す */
  int process() {
    if (ptr == order.size())
      return (-1);
    const auto id = order[ptr];
    while (nl > left[id])
      distribute(--nl);
    while (nr < right[id])
      distribute(nr++);
    while (nl < left[id])
      distribute(nl++);
    while (nr > right[id])
      distribute(--nr);
    return (order[ptr++]);
  }

  inline void distribute(int idx) {
    v[idx].flip();
    if (v[idx])
      add(idx);
    else
      del(idx);
  }

  void add(int idx);

  void del(int idx);
};
int N, A[300000], Q;
int ans[200000];
int cnt[1000001], sum;

void Mo::add(int idx) {
  if (cnt[A[idx]]++ == 0)
    ++sum;
}

void Mo::del(int idx) {
  if (--cnt[A[idx]] == 0)
    --sum;
}

int main() {
  scanf("%d", &N);
  scanf("%d", &Q);
  for (int i = 0; i < N; i++) {
    scanf("%d", &A[i]);
  }

  Mo mo(N);
  for (int i = 0; i < Q; i++) {
    int a, b;
    scanf("%d %d", &a, &b);
    mo.insert(--a, b);
  }
  mo.build();
  for (int i = 0; i < Q; i++) {
    ans[mo.process()] = sum;
  }
  for (int i = 0; i < Q; i++) {
    printf("%d\\n", ans[i]);
  }
}