Problem p03096 (C++)

Buggy submission (status: Runtime Error):
#ifdef LOCAL
// #define _GLIBCXX_DEBUG
//  #pragma comment(linker, "/STACK:102400000,102400000") // 在 Windows 上有效
#endif
// #pragma GCC optimize ("Ofast") // Ofast 等效于 -O3 -ffast-math
#include <bits/stdc++.h>

using namespace std;
#define sq(x) (x) * (x) // square
#define FAST_READ                                                              \
  ios::sync_with_stdio(false);                                                 \
  cin.tie(nullptr);
#ifdef LOCAL
#define see(x) cout << "<DBG> " << #x << ": " << (x) << endl
#endif
#ifndef LOCAL
#define see(x)
#endif
#define LSON(x) ((x)*2)
#define RSON(x) ((x)*2 + 1)
template <typename A, typename B> void Min(A &a, const B &b) {
  if (b < a)
    a = b;
}
template <typename A, typename B> void Max(A &a, const B &b) {
  if (b > a)
    a = b;
}

#if __cplusplus < 201402L
template <class Iterator>
std::reverse_iterator<Iterator> make_reverse_iterator(Iterator it) {
  return std::reverse_iterator<Iterator>(it);
}
#endif

template <typename iter_t> struct iter_pair {
  iter_t _beg, _end;
  iter_t begin() { return _beg; }
  iter_t end() { return _end; }
};

template <class cont>
iter_pair<reverse_iterator<decltype(begin(declval<cont>()))>>
reverse(cont &&r) {
  return {make_reverse_iterator(end(r)), make_reverse_iterator(begin(r))};
}

template <typename T> void dprintln(const T &t) {
  cout << t << endl;
} // for debug use
template <typename T, typename... Args>
void dprintln(const T &t, const Args &...rest) {
  cout << t << ' ';
  dprintln(rest...);
}
template <typename T> void println(const T &t) { cout << t << '\n'; }

template <typename vec_t> void println_vec(const vec_t &vec) {
  for (const auto &ele : vec) {
    cout << ele << ' ';
  }
  cout << endl;
}

template <typename T, typename... Args>
void println(const T &t, const Args &...rest) {
  cout << t << ' ';
  println(rest...);
}
template <typename T> void println(const vector<T> &vec) {
  for (const T &x : vec) {
    cout << x << ' ';
  }
  cout << endl;
}

template <typename T> void print(const T &t) { cout << t << ' '; }

template <typename T, typename... Args>
void print(const T &t, const Args &...rest) {
  cout << t << ' ';
  print(rest...);
}

// this overload is chosen when there's only one argument
template <class T> void scan(T &t) { cin >> t; }
template <class T, class... Args> void scan(T &a, Args &...rest) {
  cin >> a;
  scan(rest...);
}
template <typename T> void read(vector<T> &vec) {
  for (auto &x : vec)
    cin >> x;
}
using ull = unsigned long long;
using ll = long long;
using ul = unsigned long;
using vl = vector<ll>;
using vi = vector<int>;
using pii = pair<int, int>;
using vb = vector<bool>;
using vpii = vector<pii>;
template <typename int_t> inline int_t lowbit(int_t x) { return x & -x; }
#define rng(i, a, b) for (int i = (int)(a); i < (int)(b); ++i)
#define up(i, b, a) for (int i = int(b); i <= int(a); ++i)
#define down(i, b, a) for (int i = int(b); i >= int(a); i--)
#define rep(n) for (int _ = 0, __ = (int)n; _ < __; _++)
#define stp(i, a, b, c) for (int i = (a); i < (b); i += (c))
#define FOR(x, cont) for (const auto &x : cont)
#define INC(init, x, y) for (init; x <= y; ++x)
#define For(x, cont) for (auto &x : cont)
#define all(x) begin(x), end(x)
#define pb push_back
#define mp make_pair
#define eb emplace_back
#define SZ(x) (int)(x).size()
#define UP(i, l, r) for (i = decltype(i)(l); i <= decltype(i)(r); ++i)
#define DOWN(i, r, l) for (i = decltype(i)(r); i >= decltype(i)(l); --i)
#define Dec(a, b) for (; a >= b; --a)
template <typename T, typename Comp = less<T>>
using pq = priority_queue<T, vector<T>, Comp>;
#define popcnt(x) __builtin_popcountll((x))
#define SET(arr, v) memset(arr, (v), sizeof(arr))
#define UNIQ(vec) (vec).erase(unique(all(vec)), end(vec))
#define LB(cont, x) int(lower_bound(all(cont), x) - begin(cont))
#define UB(cont, x) int(upper_bound(all(cont), x) - begin(cont))
#define AI(name, n, m) vv<int> name(n, vi(m));
#define AL(name, n, m) vv<ll> name(size_t(n), vl(size_t(m)));
auto bet = [](const ll x, const ll y, const ll i) { return x <= i && i <= y; };

template <typename T1, typename T2>
T1 ceil(T1 x, T2 y) { // y >= 1，是整数。需要注意 x + y - 1 是否会溢出
  return (x + y - 1) / y;
}

inline int h_bit(unsigned long long x) {
  return sizeof(unsigned long long) * 8 - 1 - __builtin_clzll(x);
}

int pow2(int x) { // power of 2
  return 1 << (h_bit((ull)x) + (x != lowbit(x)));
}

template <typename T> struct bit {
  vector<T> a;
  function<T(T, T)> bin_op;
  explicit bit(int n, function<T(T, T)> bin_op, T init) : bin_op(bin_op) {
    a.resize((size_t)n + 1);
    for (int i = 1; i <= n; ++i)
      a[i] = init;
  }

  T prefix(T x, T init) {
    while (x) {
      init = bin_op(a[x], init);
      x -= x & -x;
    }
    return init;
  }

  T sum(int l, int r) {
    if (l > r)
      return 0;
    return sum(r) - sum(l - 1);
  }

  void modify(int x, T v) {
    while (x < a.size()) {
      a[x] = bin_op(a[x], v);
      x += x & -x;
    }
  }
  void clear() { fill(a.begin(), a.end(), 0); }
};

template <typename T> struct r_bit {
  vector<T> a;
  function<T(T, T)> bin_op;
  explicit r_bit(int n, function<T(T, T)> bin_op, T init)
      : bin_op(move(bin_op)) {
    a.resize((size_t)n + 1);
    for (int i = 1; i <= n; ++i)
      a[i] = init;
  }

  T suffix(int x, T init) {
    while (x < SZ(a)) {
      init = bin_op(init, a[x]);
      //            res += a[x];
      x += x & -x;
    }
    return init;
  }

  T sum(int l, int r) {
    if (l > r)
      return 0;
    return sum(r) - sum(l - 1);
  }

  void modify(int x, T v) {
    while (x > 0) {
      a[x] = bin_op(a[x], v);
      x -= x & -x;
    }
  }
  void clear() { fill(a.begin(), a.end(), 0); }
};

vi get_prime(int n) {
  vi minp((ul)n + 1), p;
  for (int i = 2; i <= n; i++) {
    if (!minp[i]) {
      minp[i] = i;
      p.pb(i);
    }
    FOR(x, p) {
      if (x <= minp[i] && x * i <= n)
        minp[x * i] = x;
      else
        break;
    }
  }
  return p;
}

const int mod = 1e9 + 7; // 记住 mod 的行号！

inline void mul(int &x, const int y) { x = int(ll(x) * y % mod); }
inline int Mul(int x, const int y) { return (int)(ll(x) * y % mod); }
template <typename T, typename U> inline void add(T &x, const U y) {
  x += y;
  if (x >= mod)
    x -= mod;
}

inline int Add(int x, int y) {
  x += y;
  if (x >= mod)
    x -= mod;
  return x;
}
inline int Sub(int x, int y) {
  x -= y;
  if (x < 0)
    x += mod;
  return x;
}
inline ll submod(ll x, ll y) { return x >= y ? x - y : x - y + mod; }
inline ll addmod(ll x, ll y) {
  x += y;
  return x >= mod ? x - mod : x;
}

inline void sub_mod(ll &x, const ll y) {
  x -= y;
  if (x < 0)
    x += mod;
}
// alias templates
template <typename T> using vv = vector<vector<T>>;
template <typename T1, typename T2 = T1> using vp = vector<pair<T1, T2>>;
template <typename T, int n> using va = vector<array<T, n>>;

#ifdef __GNUC__
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
template <typename T>
using rank_tree =
    __gnu_pbds::tree<T, __gnu_pbds::null_type, less<T>, __gnu_pbds::rb_tree_tag,
                     __gnu_pbds::tree_order_statistics_node_update>;
#endif

// union-find 并查集
struct UF {
  vi par, sz;
  int n_tree;
  explicit UF(int n) { // 0-indexed
    par.assign(n, 0);
    sz.assign(n, 1);
    rng(i, 0, n) par[i] = i;
    n_tree = n;
  }
  int n_cluster() const { return n_tree; }
  int size(int x) { return sz[root(x)]; }
  int root(int x) { return x == par[x] ? x : par[x] = root(par[x]); }
  bool unite(int x, int y) {
    int rx = root(x), ry = root(y);
    if (rx != ry) {
      par[rx] = ry;
      --n_tree;
      sz[ry] += sz[rx];
      return true;
    }
    return false;
  }
};

int fp(int x, ll n) { // fast power: hat off to quailty
  if (n < 0) {
    x = fp(x, mod - 2);
    n = -n;
  }
  int ans = 1;
  while (n) {
    if (n & 1)
      mul(ans, x);
    n /= 2;
    mul(x, x);
  }
  return ans;
}

using idx_t = long;
template <typename T, typename Compare = std::less<T>> struct ST {
  size_t n{}; // 0-indexed
  vv<T> a;
  ST() = default;
  template <typename ptr_t> ST(ptr_t beg, ptr_t end) : n(end - beg) {
    a.resize((size_t)h_bit(n) + 1); // 注意：不能写成 h_bit(n)
    a[0].assign(beg, end);
    rng(i, 0, SZ(a) - 1) {
      a[i + 1].resize(n);
      rng(j, 0, n - (1 << i)) {
        a[i + 1][j] = min(a[i][j], a[i][j + (1 << i)], Compare());
      }
      rng(j, n - (1 << i), n) { a[i + 1][j] = a[i][j]; }
    }
  }

  T query(idx_t l, idx_t r) { // l <=  r
    int i = h_bit(r - l + 1ul);
    return min(a[i][l], a[i][r + 1 - (1 << i)], Compare());
  }
};

vi get_popcnt(int n) {
  vi res((ul)n + 1);
  rng(i, 0, n) {
    if (i * 2 <= n)
      res[i * 2] = res[i];
    if ((i & 1) == 0)
      res[i + 1] = res[i] + 1;
  }
  return res;
}

using poly = vector<int>;

void bit_reverse_swap(vector<int> &a) {
  int n = SZ(a);
  for (int i = 1, j = n >> 1, k; i < n - 1; i++) {
    if (i < j)
      swap(a[i], a[j]);
    // tricky
    for (k = n >> 1; j >= k; j -= k, k >>= 1)
      ; // inspect the highest "1"
    j += k;
  }
}

void FFT(vector<int> &a, int type) {
  bit_reverse_swap(a);
  int n = SZ(a);
  for (int i = 2; i <= n; i *= 2) {
    const auto wi = fp(3, type * (mod - 1) / i); // i次单位根
    for (int j = 0; j < n; j += i) {
      auto w(1);
      for (int k = j, h = i >> 1; k < j + h; k++) {
        auto t = Mul(w, a[k + h]), u = a[k];
        a[k] = Add(u, t);
        a[k + h] = Sub(u, t);
        mul(w, wi);
      }
    }
  }
  const int inv = fp(n, -1);
  if (type == -1)
    for (auto &x : a)
      mul(x, inv);
}

void fp(poly &a, const int n) {
  a.resize((ul)pow2((SZ(a) - 1) * n + 1));
  FFT(a, 1);
  for (auto &x : a)
    x = fp(x, n);
  FFT(a, -1);
}
// DEBUG code by tourist
string to_string(const string &s) { return '"' + s + '"'; }

string to_string(const char *s) { return to_string((string)s); }

string to_string(bool b) { return (b ? "true" : "false"); }

template <typename A, typename B> string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}

template <typename A> string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto &x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}

void debug_out() { cerr << endl; }

template <typename Head, typename... Tail> void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}

#ifdef LOCAL
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define debug(...) 42
#endif
// end DEBUG
//////////////////*^"^*/////////////////////////////////////

struct node {
  static const int sigma_size = 2;
  array<int, sigma_size> pos{};
  bool is_accept_state = false;
  int suffix_pos = 0;
};

vector<node> trie;
void insert(const int *s, int len) {
  int cur = 0;
  rng(i, 0, len) {
    if (!trie[cur].pos[s[i]]) {
      trie[cur].pos[s[i]] = SZ(trie);
      trie.pb({});
    }
    cur = trie[cur].pos[s[i]];
  }
  trie[cur].is_accept_state = true;
}

void build_AC_automata() {
  queue<int> que;
  for (int i = 0; i < node::sigma_size; ++i) {
    if (trie[0].pos[i]) {
      que.push(trie[0].pos[i]);
    }
  }
  while (!que.empty()) {
    auto par = que.front();
    que.pop();
    rng(c, 0, node::sigma_size) {
      if (!trie[par].pos[c]) {
        trie[par].pos[c] = trie[trie[par].suffix_pos].pos[c];
      } else {
        int u = trie[par].pos[c];
        que.push(u);
        trie[u].suffix_pos = trie[trie[par].suffix_pos].pos[c];
      }
    }
  }
}

int main() {
  FAST_READ
#ifdef LOCAL
  cout << fixed << setprecision(10);
  ifstream in("main.in");
  cin.rdbuf(in.rdbuf());
#endif

  int n;
  scan(n);
  vi c;
  rng(i, 0, n) {
    int x;
    scan(x);
    if (c.empty() || x != c.back()) {
      c.pb(x);
    }
  }

  int m = SZ(c);
  vl sum(n + 1);

  sum[c[m - 1]] = 1;
  down(i, m - 1, 0) {
    ll t = sum[c[i]];
    if (i != 0) {
      add(sum[c[i - 1]], t);
    }
  }
  println(sum[c[0]]);

#ifdef LOCAL
  cout << "Time elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << " s.\n";
#endif
  return 0;
}


Fixed submission:
#ifdef LOCAL
// #define _GLIBCXX_DEBUG
//  #pragma comment(linker, "/STACK:102400000,102400000") // 在 Windows 上有效
#endif
// #pragma GCC optimize ("Ofast") // Ofast 等效于 -O3 -ffast-math
#include <bits/stdc++.h>

using namespace std;
#define sq(x) (x) * (x) // square
#define FAST_READ                                                              \
  ios::sync_with_stdio(false);                                                 \
  cin.tie(nullptr);
#ifdef LOCAL
#define see(x) cout << "<DBG> " << #x << ": " << (x) << endl
#endif
#ifndef LOCAL
#define see(x)
#endif
#define LSON(x) ((x)*2)
#define RSON(x) ((x)*2 + 1)
template <typename A, typename B> void Min(A &a, const B &b) {
  if (b < a)
    a = b;
}
template <typename A, typename B> void Max(A &a, const B &b) {
  if (b > a)
    a = b;
}

#if __cplusplus < 201402L
template <class Iterator>
std::reverse_iterator<Iterator> make_reverse_iterator(Iterator it) {
  return std::reverse_iterator<Iterator>(it);
}
#endif

template <typename iter_t> struct iter_pair {
  iter_t _beg, _end;
  iter_t begin() { return _beg; }
  iter_t end() { return _end; }
};

template <class cont>
iter_pair<reverse_iterator<decltype(begin(declval<cont>()))>>
reverse(cont &&r) {
  return {make_reverse_iterator(end(r)), make_reverse_iterator(begin(r))};
}

template <typename T> void dprintln(const T &t) {
  cout << t << endl;
} // for debug use
template <typename T, typename... Args>
void dprintln(const T &t, const Args &...rest) {
  cout << t << ' ';
  dprintln(rest...);
}
template <typename T> void println(const T &t) { cout << t << '\n'; }

template <typename vec_t> void println_vec(const vec_t &vec) {
  for (const auto &ele : vec) {
    cout << ele << ' ';
  }
  cout << endl;
}

template <typename T, typename... Args>
void println(const T &t, const Args &...rest) {
  cout << t << ' ';
  println(rest...);
}
template <typename T> void println(const vector<T> &vec) {
  for (const T &x : vec) {
    cout << x << ' ';
  }
  cout << endl;
}

template <typename T> void print(const T &t) { cout << t << ' '; }

template <typename T, typename... Args>
void print(const T &t, const Args &...rest) {
  cout << t << ' ';
  print(rest...);
}

// this overload is chosen when there's only one argument
template <class T> void scan(T &t) { cin >> t; }
template <class T, class... Args> void scan(T &a, Args &...rest) {
  cin >> a;
  scan(rest...);
}
template <typename T> void read(vector<T> &vec) {
  for (auto &x : vec)
    cin >> x;
}
using ull = unsigned long long;
using ll = long long;
using ul = unsigned long;
using vl = vector<ll>;
using vi = vector<int>;
using pii = pair<int, int>;
using vb = vector<bool>;
using vpii = vector<pii>;
template <typename int_t> inline int_t lowbit(int_t x) { return x & -x; }
#define rng(i, a, b) for (int i = (int)(a); i < (int)(b); ++i)
#define up(i, b, a) for (int i = int(b); i <= int(a); ++i)
#define down(i, b, a) for (int i = int(b); i >= int(a); i--)
#define rep(n) for (int _ = 0, __ = (int)n; _ < __; _++)
#define stp(i, a, b, c) for (int i = (a); i < (b); i += (c))
#define FOR(x, cont) for (const auto &x : cont)
#define INC(init, x, y) for (init; x <= y; ++x)
#define For(x, cont) for (auto &x : cont)
#define all(x) begin(x), end(x)
#define pb push_back
#define mp make_pair
#define eb emplace_back
#define SZ(x) (int)(x).size()
#define UP(i, l, r) for (i = decltype(i)(l); i <= decltype(i)(r); ++i)
#define DOWN(i, r, l) for (i = decltype(i)(r); i >= decltype(i)(l); --i)
#define Dec(a, b) for (; a >= b; --a)
template <typename T, typename Comp = less<T>>
using pq = priority_queue<T, vector<T>, Comp>;
#define popcnt(x) __builtin_popcountll((x))
#define SET(arr, v) memset(arr, (v), sizeof(arr))
#define UNIQ(vec) (vec).erase(unique(all(vec)), end(vec))
#define LB(cont, x) int(lower_bound(all(cont), x) - begin(cont))
#define UB(cont, x) int(upper_bound(all(cont), x) - begin(cont))
#define AI(name, n, m) vv<int> name(n, vi(m));
#define AL(name, n, m) vv<ll> name(size_t(n), vl(size_t(m)));
auto bet = [](const ll x, const ll y, const ll i) { return x <= i && i <= y; };

template <typename T1, typename T2>
T1 ceil(T1 x, T2 y) { // y >= 1，是整数。需要注意 x + y - 1 是否会溢出
  return (x + y - 1) / y;
}

inline int h_bit(unsigned long long x) {
  return sizeof(unsigned long long) * 8 - 1 - __builtin_clzll(x);
}

int pow2(int x) { // power of 2
  return 1 << (h_bit((ull)x) + (x != lowbit(x)));
}

template <typename T> struct bit {
  vector<T> a;
  function<T(T, T)> bin_op;
  explicit bit(int n, function<T(T, T)> bin_op, T init) : bin_op(bin_op) {
    a.resize((size_t)n + 1);
    for (int i = 1; i <= n; ++i)
      a[i] = init;
  }

  T prefix(T x, T init) {
    while (x) {
      init = bin_op(a[x], init);
      x -= x & -x;
    }
    return init;
  }

  T sum(int l, int r) {
    if (l > r)
      return 0;
    return sum(r) - sum(l - 1);
  }

  void modify(int x, T v) {
    while (x < a.size()) {
      a[x] = bin_op(a[x], v);
      x += x & -x;
    }
  }
  void clear() { fill(a.begin(), a.end(), 0); }
};

template <typename T> struct r_bit {
  vector<T> a;
  function<T(T, T)> bin_op;
  explicit r_bit(int n, function<T(T, T)> bin_op, T init)
      : bin_op(move(bin_op)) {
    a.resize((size_t)n + 1);
    for (int i = 1; i <= n; ++i)
      a[i] = init;
  }

  T suffix(int x, T init) {
    while (x < SZ(a)) {
      init = bin_op(init, a[x]);
      //            res += a[x];
      x += x & -x;
    }
    return init;
  }

  T sum(int l, int r) {
    if (l > r)
      return 0;
    return sum(r) - sum(l - 1);
  }

  void modify(int x, T v) {
    while (x > 0) {
      a[x] = bin_op(a[x], v);
      x -= x & -x;
    }
  }
  void clear() { fill(a.begin(), a.end(), 0); }
};

vi get_prime(int n) {
  vi minp((ul)n + 1), p;
  for (int i = 2; i <= n; i++) {
    if (!minp[i]) {
      minp[i] = i;
      p.pb(i);
    }
    FOR(x, p) {
      if (x <= minp[i] && x * i <= n)
        minp[x * i] = x;
      else
        break;
    }
  }
  return p;
}

const int mod = 1e9 + 7; // 记住 mod 的行号！

inline void mul(int &x, const int y) { x = int(ll(x) * y % mod); }
inline int Mul(int x, const int y) { return (int)(ll(x) * y % mod); }
template <typename T, typename U> inline void add(T &x, const U y) {
  x += y;
  if (x >= mod)
    x -= mod;
}

inline int Add(int x, int y) {
  x += y;
  if (x >= mod)
    x -= mod;
  return x;
}
inline int Sub(int x, int y) {
  x -= y;
  if (x < 0)
    x += mod;
  return x;
}
inline ll submod(ll x, ll y) { return x >= y ? x - y : x - y + mod; }
inline ll addmod(ll x, ll y) {
  x += y;
  return x >= mod ? x - mod : x;
}

inline void sub_mod(ll &x, const ll y) {
  x -= y;
  if (x < 0)
    x += mod;
}
// alias templates
template <typename T> using vv = vector<vector<T>>;
template <typename T1, typename T2 = T1> using vp = vector<pair<T1, T2>>;
template <typename T, int n> using va = vector<array<T, n>>;

#ifdef __GNUC__
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
template <typename T>
using rank_tree =
    __gnu_pbds::tree<T, __gnu_pbds::null_type, less<T>, __gnu_pbds::rb_tree_tag,
                     __gnu_pbds::tree_order_statistics_node_update>;
#endif

// union-find 并查集
struct UF {
  vi par, sz;
  int n_tree;
  explicit UF(int n) { // 0-indexed
    par.assign(n, 0);
    sz.assign(n, 1);
    rng(i, 0, n) par[i] = i;
    n_tree = n;
  }
  int n_cluster() const { return n_tree; }
  int size(int x) { return sz[root(x)]; }
  int root(int x) { return x == par[x] ? x : par[x] = root(par[x]); }
  bool unite(int x, int y) {
    int rx = root(x), ry = root(y);
    if (rx != ry) {
      par[rx] = ry;
      --n_tree;
      sz[ry] += sz[rx];
      return true;
    }
    return false;
  }
};

int fp(int x, ll n) { // fast power: hat off to quailty
  if (n < 0) {
    x = fp(x, mod - 2);
    n = -n;
  }
  int ans = 1;
  while (n) {
    if (n & 1)
      mul(ans, x);
    n /= 2;
    mul(x, x);
  }
  return ans;
}

using idx_t = long;
template <typename T, typename Compare = std::less<T>> struct ST {
  size_t n{}; // 0-indexed
  vv<T> a;
  ST() = default;
  template <typename ptr_t> ST(ptr_t beg, ptr_t end) : n(end - beg) {
    a.resize((size_t)h_bit(n) + 1); // 注意：不能写成 h_bit(n)
    a[0].assign(beg, end);
    rng(i, 0, SZ(a) - 1) {
      a[i + 1].resize(n);
      rng(j, 0, n - (1 << i)) {
        a[i + 1][j] = min(a[i][j], a[i][j + (1 << i)], Compare());
      }
      rng(j, n - (1 << i), n) { a[i + 1][j] = a[i][j]; }
    }
  }

  T query(idx_t l, idx_t r) { // l <=  r
    int i = h_bit(r - l + 1ul);
    return min(a[i][l], a[i][r + 1 - (1 << i)], Compare());
  }
};

vi get_popcnt(int n) {
  vi res((ul)n + 1);
  rng(i, 0, n) {
    if (i * 2 <= n)
      res[i * 2] = res[i];
    if ((i & 1) == 0)
      res[i + 1] = res[i] + 1;
  }
  return res;
}

using poly = vector<int>;

void bit_reverse_swap(vector<int> &a) {
  int n = SZ(a);
  for (int i = 1, j = n >> 1, k; i < n - 1; i++) {
    if (i < j)
      swap(a[i], a[j]);
    // tricky
    for (k = n >> 1; j >= k; j -= k, k >>= 1)
      ; // inspect the highest "1"
    j += k;
  }
}

void FFT(vector<int> &a, int type) {
  bit_reverse_swap(a);
  int n = SZ(a);
  for (int i = 2; i <= n; i *= 2) {
    const auto wi = fp(3, type * (mod - 1) / i); // i次单位根
    for (int j = 0; j < n; j += i) {
      auto w(1);
      for (int k = j, h = i >> 1; k < j + h; k++) {
        auto t = Mul(w, a[k + h]), u = a[k];
        a[k] = Add(u, t);
        a[k + h] = Sub(u, t);
        mul(w, wi);
      }
    }
  }
  const int inv = fp(n, -1);
  if (type == -1)
    for (auto &x : a)
      mul(x, inv);
}

void fp(poly &a, const int n) {
  a.resize((ul)pow2((SZ(a) - 1) * n + 1));
  FFT(a, 1);
  for (auto &x : a)
    x = fp(x, n);
  FFT(a, -1);
}
// DEBUG code by tourist
string to_string(const string &s) { return '"' + s + '"'; }

string to_string(const char *s) { return to_string((string)s); }

string to_string(bool b) { return (b ? "true" : "false"); }

template <typename A, typename B> string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}

template <typename A> string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto &x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}

void debug_out() { cerr << endl; }

template <typename Head, typename... Tail> void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}

#ifdef LOCAL
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define debug(...) 42
#endif
// end DEBUG
//////////////////*^"^*/////////////////////////////////////

struct node {
  static const int sigma_size = 2;
  array<int, sigma_size> pos{};
  bool is_accept_state = false;
  int suffix_pos = 0;
};

vector<node> trie;
void insert(const int *s, int len) {
  int cur = 0;
  rng(i, 0, len) {
    if (!trie[cur].pos[s[i]]) {
      trie[cur].pos[s[i]] = SZ(trie);
      trie.pb({});
    }
    cur = trie[cur].pos[s[i]];
  }
  trie[cur].is_accept_state = true;
}

void build_AC_automata() {
  queue<int> que;
  for (int i = 0; i < node::sigma_size; ++i) {
    if (trie[0].pos[i]) {
      que.push(trie[0].pos[i]);
    }
  }
  while (!que.empty()) {
    auto par = que.front();
    que.pop();
    rng(c, 0, node::sigma_size) {
      if (!trie[par].pos[c]) {
        trie[par].pos[c] = trie[trie[par].suffix_pos].pos[c];
      } else {
        int u = trie[par].pos[c];
        que.push(u);
        trie[u].suffix_pos = trie[trie[par].suffix_pos].pos[c];
      }
    }
  }
}

int main() {
  FAST_READ
#ifdef LOCAL
  cout << fixed << setprecision(10);
  ifstream in("main.in");
  cin.rdbuf(in.rdbuf());
#endif

  int n;
  scan(n);
  vi c;
  rng(i, 0, n) {
    int x;
    scan(x);
    if (c.empty() || x != c.back()) {
      c.pb(x);
    }
  }

  int m = SZ(c);

  vl sum(*max_element(all(c)) + 1);

  sum[c[m - 1]] = 1;
  down(i, m - 1, 0) {
    ll t = sum[c[i]];
    if (i != 0) {
      add(sum[c[i - 1]], t);
    }
  }
  println(sum[c[0]]);

#ifdef LOCAL
  cout << "Time elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << " s.\n";
#endif
  return 0;
}