Problem p03096 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <cmath>
#include <cstring>
#include <functional>
#include <iomanip>
#include <iostream>
#include <limits>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>

using namespace std;

#ifdef LOCAL
#define eprintf(...) fprintf(stderr, __VA_ARGS__)
#else
#define eprintf(...) 42
#endif
using ll = long long;
using vll = std::vector<ll>;
using vvll = std::vector<vll>;
using vvvll = std::vector<vvll>;
#define reps(i, S, E) for (ll i = (S); i <= (E); i++)
#define rep(i, N) reps(i, 0, N - 1)
#define deps(i, E, S) for (ll i = (E); i >= (S); i--)
#define dep(i, N) deps(i, N - 1, 0)
const ll INF = 1LL << 60;
const int INF_INT = 1 << 30;

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;
}
struct mll {
  static ll MOD;
  ll val;
  mll(ll v = 0) : val(v % MOD) {
    if (val < 0)
      val += MOD;
  }
  mll operator-() const { return -val; }
  mll operator+(const mll &b) const { return val + b.val; }
  mll operator-(const mll &b) const { return val - b.val; }
  mll operator*(const mll &b) const { return val * b.val; }
  mll operator/(const mll &b) const { return mll(*this) /= b; }
  mll operator+(ll b) const { return *this + mll(b); }
  mll operator-(ll b) const { return *this - mll(b); }
  mll operator*(ll b) const { return *this * mll(b); }
  friend mll operator+(ll a, const mll &b) { return b + a; }
  friend mll operator-(ll a, const mll &b) { return -b + a; }
  friend mll operator*(ll a, const mll &b) { return b * a; }
  mll &operator+=(const mll &b) {
    val = (val + b.val) % MOD;
    return *this;
  }
  mll &operator-=(const mll &b) {
    val = (val + MOD - b.val) % MOD;
    return *this;
  }
  mll &operator*=(const mll &b) {
    val = (val * b.val) % MOD;
    return *this;
  }
  mll &operator/=(const mll &b) {
    ll c = b.val, d = MOD, u = 1, v = 0;
    while (d) {
      ll t = c / d;
      c -= t * d;
      swap(c, d);
      u -= t * v;
      swap(u, v);
    }
    val = val * u % MOD;
    if (val < 0)
      val += MOD;
    return *this;
  }
  mll &operator+=(ll b) { return *this += mll(b); }
  mll &operator-=(ll b) { return *this -= mll(b); }
  mll &operator*=(ll b) { return *this *= mll(b); }
  mll &operator/=(ll b) { return *this /= mll(b); }
  bool operator==(const mll &b) { return val == b.val; }
  bool operator!=(const mll &b) { return val != b.val; }
  bool operator==(ll b) { return *this == mll(b); }
  bool operator!=(ll b) { return *this != mll(b); }
  friend bool operator==(ll a, const mll &b) { return mll(a) == b.val; }
  friend bool operator!=(ll a, const mll &b) { return mll(a) != b.val; }
  friend ostream &operator<<(ostream &os, const mll &a) { return os << a.val; }
  friend istream &operator>>(istream &is, mll &a) { return is >> a.val; }
  static mll Combination(ll a, ll b) {
    chmin(b, a - b);
    if (b < 0)
      return mll(0);
    mll c = 1;
    rep(i, b) c *= a - i;
    rep(i, b) c /= i + 1;
    return c;
  }
};
using vmll = std::vector<mll>;
using vvmll = std::vector<vmll>;
using vvvmll = std::vector<vvmll>;
using vvvvmll = std::vector<vvvmll>;

struct Fast {
  Fast() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(std::numeric_limits<double>::max_digits10);
  }
} fast; // cin,cout高速化のおまじない＋桁数指定

ll mll::MOD = (ll)(1e9 + 7); // 998244353ll;

int main() {
  ll N;
  cin >> N;
  vector<ll> C(N);
  rep(i, N) { cin >> C[i]; }

  vll prevC(20010, -1);
  vmll dp(N, 0);
  dp[0] = 1;

  rep(i, N) {
    if (i > 0) {
      dp[i] += dp[i - 1];
      if (prevC[C[i]] >= 0 && prevC[C[i]] + 1 < i) {
        dp[i] += dp[prevC[C[i]]];
      }
    }
    prevC[C[i]] = i;
  }

  cout << dp[N - 1] << endl;

  return 0;
}


Fixed submission:
#include <algorithm>
#include <cmath>
#include <cstring>
#include <functional>
#include <iomanip>
#include <iostream>
#include <limits>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>

using namespace std;

#ifdef LOCAL
#define eprintf(...) fprintf(stderr, __VA_ARGS__)
#else
#define eprintf(...) 42
#endif
using ll = long long;
using vll = std::vector<ll>;
using vvll = std::vector<vll>;
using vvvll = std::vector<vvll>;
#define reps(i, S, E) for (ll i = (S); i <= (E); i++)
#define rep(i, N) reps(i, 0, N - 1)
#define deps(i, E, S) for (ll i = (E); i >= (S); i--)
#define dep(i, N) deps(i, N - 1, 0)
const ll INF = 1LL << 60;
const int INF_INT = 1 << 30;

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;
}
struct mll {
  static ll MOD;
  ll val;
  mll(ll v = 0) : val(v % MOD) {
    if (val < 0)
      val += MOD;
  }
  mll operator-() const { return -val; }
  mll operator+(const mll &b) const { return val + b.val; }
  mll operator-(const mll &b) const { return val - b.val; }
  mll operator*(const mll &b) const { return val * b.val; }
  mll operator/(const mll &b) const { return mll(*this) /= b; }
  mll operator+(ll b) const { return *this + mll(b); }
  mll operator-(ll b) const { return *this - mll(b); }
  mll operator*(ll b) const { return *this * mll(b); }
  friend mll operator+(ll a, const mll &b) { return b + a; }
  friend mll operator-(ll a, const mll &b) { return -b + a; }
  friend mll operator*(ll a, const mll &b) { return b * a; }
  mll &operator+=(const mll &b) {
    val = (val + b.val) % MOD;
    return *this;
  }
  mll &operator-=(const mll &b) {
    val = (val + MOD - b.val) % MOD;
    return *this;
  }
  mll &operator*=(const mll &b) {
    val = (val * b.val) % MOD;
    return *this;
  }
  mll &operator/=(const mll &b) {
    ll c = b.val, d = MOD, u = 1, v = 0;
    while (d) {
      ll t = c / d;
      c -= t * d;
      swap(c, d);
      u -= t * v;
      swap(u, v);
    }
    val = val * u % MOD;
    if (val < 0)
      val += MOD;
    return *this;
  }
  mll &operator+=(ll b) { return *this += mll(b); }
  mll &operator-=(ll b) { return *this -= mll(b); }
  mll &operator*=(ll b) { return *this *= mll(b); }
  mll &operator/=(ll b) { return *this /= mll(b); }
  bool operator==(const mll &b) { return val == b.val; }
  bool operator!=(const mll &b) { return val != b.val; }
  bool operator==(ll b) { return *this == mll(b); }
  bool operator!=(ll b) { return *this != mll(b); }
  friend bool operator==(ll a, const mll &b) { return mll(a) == b.val; }
  friend bool operator!=(ll a, const mll &b) { return mll(a) != b.val; }
  friend ostream &operator<<(ostream &os, const mll &a) { return os << a.val; }
  friend istream &operator>>(istream &is, mll &a) { return is >> a.val; }
  static mll Combination(ll a, ll b) {
    chmin(b, a - b);
    if (b < 0)
      return mll(0);
    mll c = 1;
    rep(i, b) c *= a - i;
    rep(i, b) c /= i + 1;
    return c;
  }
};
using vmll = std::vector<mll>;
using vvmll = std::vector<vmll>;
using vvvmll = std::vector<vvmll>;
using vvvvmll = std::vector<vvvmll>;

struct Fast {
  Fast() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(std::numeric_limits<double>::max_digits10);
  }
} fast; // cin,cout高速化のおまじない＋桁数指定

ll mll::MOD = (ll)(1e9 + 7); // 998244353ll;

int main() {
  ll N;
  cin >> N;
  vector<ll> C(N);
  rep(i, N) { cin >> C[i]; }

  vll prevC(200010, -1);
  vmll dp(N, 0);
  dp[0] = 1;

  rep(i, N) {
    if (i > 0) {
      dp[i] += dp[i - 1];
      if (prevC[C[i]] >= 0 && prevC[C[i]] + 1 < i) {
        dp[i] += dp[prevC[C[i]]];
      }
    }
    prevC[C[i]] = i;
  }

  cout << dp[N - 1] << endl;

  return 0;
}