Problem p03096 (C++)

Buggy submission (status: Runtime Error):
#include "bits/stdc++.h"

using namespace std;
#ifdef _DEBUG
#define _GLIBCXX_DEBUG
#include "dump.hpp"
#else
#define dump(...)
#endif

#define int long long
#define ll long long
#define ll1 1ll
#define ONE 1ll
#define DBG 1
#define rep(i, a, b) for (int i = (a); i < (b); i++)
#define rrep(i, a, b) for (int i = (b)-1; i >= (a); i--)
#define loop(n) rep(loop, (0), (n))
#define all(c) begin(c), end(c)
const int INF =
    sizeof(int) == sizeof(long long) ? 0x3f3f3f3f3f3f3f3fLL : 0x3f3f3f3f;
const int MOD = (int)(1e9) + 7;
const double PI = acos(-1);
const double EPS = 1e-9;
#define fi first
#define se second
#define pb push_back
#define eb emplace_back
using pii = pair<int, int>;
// template<class T> ostream &operator<<(ostream &os,T &t){dump(t);return os;}
template <typename T, typename S>
istream &operator>>(istream &is, pair<T, S> &p) {
  is >> p.first >> p.second;
  return is;
}
template <typename T, typename S>
ostream &operator<<(ostream &os, pair<T, S> &p) {
  os << p.first << " " << p.second;
  return os;
}

template <typename T> void printvv(const vector<vector<T>> &v) {
  cerr << endl;
  rep(i, 0, v.size()) rep(j, 0, v[i].size()) {
    if (typeid(v[i][j]).name() == typeid(INF).name() and v[i][j] == INF) {
      cerr << "INF";
    } else
      cerr << v[i][j];
    cerr << (j == v[i].size() - 1 ? '\n' : ' ');
  }
  cerr << endl;
}
/*
typedef __int128_t Int;
std::ostream &operator<<(std::ostream &dest, __int128_t value) {
std::ostream::sentry s(dest);
  if (s) {
        __uint128_t tmp = value < 0 ? -value : value;
        char buffer[128];
        char *d = std::end(buffer);
        do {
          --d;
          *d = "0123456789"[tmp % 10];
          tmp /= 10;
        } while (tmp != 0);
        if (value < 0) {
          --d;
          *d = '-';
        }
        int len = std::end(buffer) - d;
        if (dest.rdbuf()->sputn(d, len) != len) {
          dest.setstate(std::ios_base::badbit);
        }
  }
  return dest;
}

__int128 parse(string &s) {
  __int128 ret = 0;
  for (int i = 0; i < s.length(); i++)
        if ('0' <= s[i] && s[i] <= '9')
          ret = 10 * ret + s[i] - '0';
  return ret;
}
*/

#ifndef _DEBUG
#define printvv(...)
#endif
void YES(bool f) { cout << (f ? "YES" : "NO") << endl; }
void Yes(bool f) { cout << (f ? "Yes" : "No") << endl; }
template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <int MOD> struct ModInt {
  static const int Mod = MOD;
  unsigned x;
  ModInt() : x(0) {}
  ModInt(signed sig) {
    int sigt = sig % MOD;
    if (sigt < 0)
      sigt += MOD;
    x = sigt;
  }
  ModInt(signed long long sig) {
    int sigt = sig % MOD;
    if (sigt < 0)
      sigt += MOD;
    x = sigt;
  }
  int get() const { return (int)x; }

  ModInt &operator+=(ModInt that) {
    if ((x += that.x) >= MOD)
      x -= MOD;
    return *this;
  }
  ModInt &operator-=(ModInt that) {
    if ((x += MOD - that.x) >= MOD)
      x -= MOD;
    return *this;
  }
  ModInt &operator*=(ModInt that) {
    x = (unsigned long long)x * that.x % MOD;
    return *this;
  }
  ModInt &operator/=(ModInt that) { return *this *= that.inverse(); }

  ModInt operator+(ModInt that) const { return ModInt(*this) += that; }
  ModInt operator-(ModInt that) const { return ModInt(*this) -= that; }
  ModInt operator*(ModInt that) const { return ModInt(*this) *= that; }
  ModInt operator/(ModInt that) const { return ModInt(*this) /= that; }

  ModInt inverse() const {
    signed a = x, b = MOD, u = 1, v = 0;
    while (b) {
      signed t = a / b;
      a -= t * b;
      std::swap(a, b);
      u -= t * v;
      std::swap(u, v);
    }
    if (u < 0)
      u += MOD;
    ModInt res;
    res.x = (unsigned)u;
    return res;
  }
};
template <int MOD> ostream &operator<<(ostream &os, const ModInt<MOD> &m) {
  return os << m.x;
}
template <int MOD> istream &operator>>(istream &is, ModInt<MOD> &m) {
  signed long long s;
  is >> s;
  m = ModInt<MOD>(s);
  return is;
};
// pow(mint(2), 1000) のように
template <int MOD> ModInt<MOD> pow(ModInt<MOD> a, unsigned long long k) {
  ModInt<MOD> r = 1;
  while (k) {
    if (k & 1)
      r *= a;
    a *= a;
    k >>= 1;
  }
  return r;
}

// #define int long long を使っても大丈夫
using mint = ModInt<1000000007>;

// nCrで用いる
vector<mint> fact, factinv;
// nCrで用いる 予め計算しておく
void nCr_compute_factinv(int N) {
  N = min(N, mint::Mod - 1);
  fact.resize(N + 1);
  factinv.resize(N + 1);
  fact[0] = 1;
  rep(i, 1, N + 1) fact[i] = fact[i - 1] * i;
  factinv[N] = fact[N].inverse();
  for (int i = N; i >= 1; i--)
    factinv[i - 1] = factinv[i] * i;
}
mint nCr(int n, int r) {
  if (n >= mint::Mod)
    return nCr(n % mint::Mod, r % mint::Mod) *
           nCr(n / mint::Mod, r / mint::Mod);
  return r > n ? 0 : fact[n] * factinv[n - r] * factinv[r];
}

mint nHr(int n, int r) { return r == 0 ? 1 : nCr(n + r - 1, r); }

signed main(signed argc, char *argv[]) {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(12);

  int N;
  cin >> N;
  vector<int> C(N);
  rep(i, 0, N) {
    cin >> C[i];
    C[i]--;
  }
  vector<int> idx(N + 1, -1);
  vector<mint> dp(N + 1);
  dp[0] = 1;
  rep(i, 1, N + 1) {
    dp[i] = dp[i - 1];
    if (idx[C[i - 1]] != -1)
      assert(i - 2 >= 0);
    if (idx[C[i - 1]] != -1 and idx[C[i - 1]] != i - 1) {
      dump(idx[C[i - 1]]);
      dp[i] += dp[idx[C[i - 1]]];
    }
    idx[C[i - 1]] = i;
    dump(i, dp);
  }
  cout << dp[N] << endl;

  return 0;
}


Fixed submission:
#include "bits/stdc++.h"

using namespace std;
#ifdef _DEBUG
#define _GLIBCXX_DEBUG
#include "dump.hpp"
#else
#define dump(...)
#endif

#define int long long
#define ll long long
#define ll1 1ll
#define ONE 1ll
#define DBG 1
#define rep(i, a, b) for (int i = (a); i < (b); i++)
#define rrep(i, a, b) for (int i = (b)-1; i >= (a); i--)
#define loop(n) rep(loop, (0), (n))
#define all(c) begin(c), end(c)
const int INF =
    sizeof(int) == sizeof(long long) ? 0x3f3f3f3f3f3f3f3fLL : 0x3f3f3f3f;
const int MOD = (int)(1e9) + 7;
const double PI = acos(-1);
const double EPS = 1e-9;
#define fi first
#define se second
#define pb push_back
#define eb emplace_back
using pii = pair<int, int>;
// template<class T> ostream &operator<<(ostream &os,T &t){dump(t);return os;}
template <typename T, typename S>
istream &operator>>(istream &is, pair<T, S> &p) {
  is >> p.first >> p.second;
  return is;
}
template <typename T, typename S>
ostream &operator<<(ostream &os, pair<T, S> &p) {
  os << p.first << " " << p.second;
  return os;
}

template <typename T> void printvv(const vector<vector<T>> &v) {
  cerr << endl;
  rep(i, 0, v.size()) rep(j, 0, v[i].size()) {
    if (typeid(v[i][j]).name() == typeid(INF).name() and v[i][j] == INF) {
      cerr << "INF";
    } else
      cerr << v[i][j];
    cerr << (j == v[i].size() - 1 ? '\n' : ' ');
  }
  cerr << endl;
}
/*
typedef __int128_t Int;
std::ostream &operator<<(std::ostream &dest, __int128_t value) {
std::ostream::sentry s(dest);
  if (s) {
        __uint128_t tmp = value < 0 ? -value : value;
        char buffer[128];
        char *d = std::end(buffer);
        do {
          --d;
          *d = "0123456789"[tmp % 10];
          tmp /= 10;
        } while (tmp != 0);
        if (value < 0) {
          --d;
          *d = '-';
        }
        int len = std::end(buffer) - d;
        if (dest.rdbuf()->sputn(d, len) != len) {
          dest.setstate(std::ios_base::badbit);
        }
  }
  return dest;
}

__int128 parse(string &s) {
  __int128 ret = 0;
  for (int i = 0; i < s.length(); i++)
        if ('0' <= s[i] && s[i] <= '9')
          ret = 10 * ret + s[i] - '0';
  return ret;
}
*/

#ifndef _DEBUG
#define printvv(...)
#endif
void YES(bool f) { cout << (f ? "YES" : "NO") << endl; }
void Yes(bool f) { cout << (f ? "Yes" : "No") << endl; }
template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <int MOD> struct ModInt {
  static const int Mod = MOD;
  unsigned x;
  ModInt() : x(0) {}
  ModInt(signed sig) {
    int sigt = sig % MOD;
    if (sigt < 0)
      sigt += MOD;
    x = sigt;
  }
  ModInt(signed long long sig) {
    int sigt = sig % MOD;
    if (sigt < 0)
      sigt += MOD;
    x = sigt;
  }
  int get() const { return (int)x; }

  ModInt &operator+=(ModInt that) {
    if ((x += that.x) >= MOD)
      x -= MOD;
    return *this;
  }
  ModInt &operator-=(ModInt that) {
    if ((x += MOD - that.x) >= MOD)
      x -= MOD;
    return *this;
  }
  ModInt &operator*=(ModInt that) {
    x = (unsigned long long)x * that.x % MOD;
    return *this;
  }
  ModInt &operator/=(ModInt that) { return *this *= that.inverse(); }

  ModInt operator+(ModInt that) const { return ModInt(*this) += that; }
  ModInt operator-(ModInt that) const { return ModInt(*this) -= that; }
  ModInt operator*(ModInt that) const { return ModInt(*this) *= that; }
  ModInt operator/(ModInt that) const { return ModInt(*this) /= that; }

  ModInt inverse() const {
    signed a = x, b = MOD, u = 1, v = 0;
    while (b) {
      signed t = a / b;
      a -= t * b;
      std::swap(a, b);
      u -= t * v;
      std::swap(u, v);
    }
    if (u < 0)
      u += MOD;
    ModInt res;
    res.x = (unsigned)u;
    return res;
  }
};
template <int MOD> ostream &operator<<(ostream &os, const ModInt<MOD> &m) {
  return os << m.x;
}
template <int MOD> istream &operator>>(istream &is, ModInt<MOD> &m) {
  signed long long s;
  is >> s;
  m = ModInt<MOD>(s);
  return is;
};
// pow(mint(2), 1000) のように
template <int MOD> ModInt<MOD> pow(ModInt<MOD> a, unsigned long long k) {
  ModInt<MOD> r = 1;
  while (k) {
    if (k & 1)
      r *= a;
    a *= a;
    k >>= 1;
  }
  return r;
}

// #define int long long を使っても大丈夫
using mint = ModInt<1000000007>;

// nCrで用いる
vector<mint> fact, factinv;
// nCrで用いる 予め計算しておく
void nCr_compute_factinv(int N) {
  N = min(N, mint::Mod - 1);
  fact.resize(N + 1);
  factinv.resize(N + 1);
  fact[0] = 1;
  rep(i, 1, N + 1) fact[i] = fact[i - 1] * i;
  factinv[N] = fact[N].inverse();
  for (int i = N; i >= 1; i--)
    factinv[i - 1] = factinv[i] * i;
}
mint nCr(int n, int r) {
  if (n >= mint::Mod)
    return nCr(n % mint::Mod, r % mint::Mod) *
           nCr(n / mint::Mod, r / mint::Mod);
  return r > n ? 0 : fact[n] * factinv[n - r] * factinv[r];
}

mint nHr(int n, int r) { return r == 0 ? 1 : nCr(n + r - 1, r); }

signed main(signed argc, char *argv[]) {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(12);

  int N;
  cin >> N;
  vector<int> C(N);
  rep(i, 0, N) {
    cin >> C[i];
    C[i]--;
  }
  vector<int> idx(2 * 1e5 + 1, -1);
  vector<mint> dp(N + 1);
  dp[0] = 1;
  rep(i, 1, N + 1) {
    dp[i] = dp[i - 1];
    if (idx[C[i - 1]] != -1)
      assert(i - 2 >= 0);
    if (idx[C[i - 1]] != -1 and idx[C[i - 1]] != i - 1) {
      dump(idx[C[i - 1]]);
      dp[i] += dp[idx[C[i - 1]]];
    }
    idx[C[i - 1]] = i;
    dump(i, dp);
  }
  cout << dp[N] << endl;

  return 0;
}