Problem p03003 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;

using ll = long long;
using Pi = pair<int, int>;
using Pl = pair<ll, ll>;
using vint = vector<int>;
using vvint = vector<vint>;
using vvvint = vector<vvint>;
using vdouble = vector<double>;
using vvdouble = vector<vdouble>;
using vvvdouble = vector<vvdouble>;
using vll = vector<ll>;
using vvll = vector<vll>;
using vvvll = vector<vvll>;
using uint = unsigned int;
using ull = unsigned long long;

template <typename T> using uset = unordered_set<T>;
template <typename T1, typename T2> using umap = unordered_map<T1, T2>;

constexpr int INF = (1 << 30) - 1;
constexpr ll LLINF = 1LL << 60;
constexpr int dy[] = {1, 0, -1, 0, 1, -1, -1, 1};
constexpr int dx[] = {0, 1, 0, -1, 1, 1, -1, -1};
constexpr char el = '\n';
constexpr int mod = 1000000007;
constexpr int mod2 = 998244353;
template <typename T> T gcd(T a, T b) { return (b ? gcd(b, a % b) : a); }
template <typename T> T lcm(T a, T b) { return (a / gcd(a, b) * b); }
template <typename T1, typename T2> inline bool chmin(T1 &a, T2 b) {
  return (a > b && (a = b, true));
}
template <typename T1, typename T2> inline bool chmax(T1 &a, T2 b) {
  return (a < b && (a = b, true));
}
template <typename T> bool isin(T y, T x, T h, T w) {
  return (0 <= y && 0 <= x && y < h && x < w);
}
template <typename T> bool isin1(T y, T x, T h, T w) {
  return (0 < y && 0 < x && y <= h && x <= w);
}

template <typename T> ostream &operator<<(ostream &os, vector<T> &v) {
  os << v[0];
  for (int i = 1; i < v.size(); i++)
    os << " " << v[i];
  return (os);
}

template <typename T> istream &operator>>(istream &is, vector<T> &v) {
  for (auto &u : v)
    is >> u;
  return (is);
}

template <typename T1, typename T2>
istream &operator>>(istream &is, pair<T1, T2> &p) {
  return (is >> p.first >> p.second);
}

void Main() {
  ll N, M;
  cin >> N >> M;
  vll S(N), T(M);
  cin >> S >> T;
  vvll dp(N + 1, vll(M + 1, 0));
  dp[0][0] = 1;
  for (int i = 0; i < N; i++) {
    for (int j = 0; j <= M; j++) {
      if (j < M && S[i] == T[j])
        (dp[i + 1][j + 1] += dp[i][j]) %= mod;
      (dp[i + 1][j] += dp[i][j]) %= mod;
      (dp[i][j + 1] += dp[i][j]) %= mod;
      (dp[i + 1][j + 1] += mod - dp[i][j]) %= mod;
    }
  }
  ll sum = 0;
  for (int i = 0; i <= M; i++) {
    (sum += dp[N][i]) %= mod;
  }
  cout << sum << endl;
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(0);
  cout << fixed << setprecision(20);
  Main();
  return (0);
}


Fixed submission:
#include <bits/stdc++.h>
using namespace std;

using ll = long long;
using Pi = pair<int, int>;
using Pl = pair<ll, ll>;
using vint = vector<int>;
using vvint = vector<vint>;
using vvvint = vector<vvint>;
using vdouble = vector<double>;
using vvdouble = vector<vdouble>;
using vvvdouble = vector<vvdouble>;
using vll = vector<ll>;
using vvll = vector<vll>;
using vvvll = vector<vvll>;
using uint = unsigned int;
using ull = unsigned long long;

template <typename T> using uset = unordered_set<T>;
template <typename T1, typename T2> using umap = unordered_map<T1, T2>;

constexpr int INF = (1 << 30) - 1;
constexpr ll LLINF = 1LL << 60;
constexpr int dy[] = {1, 0, -1, 0, 1, -1, -1, 1};
constexpr int dx[] = {0, 1, 0, -1, 1, 1, -1, -1};
constexpr char el = '\n';
constexpr int mod = 1000000007;
constexpr int mod2 = 998244353;
template <typename T> T gcd(T a, T b) { return (b ? gcd(b, a % b) : a); }
template <typename T> T lcm(T a, T b) { return (a / gcd(a, b) * b); }
template <typename T1, typename T2> inline bool chmin(T1 &a, T2 b) {
  return (a > b && (a = b, true));
}
template <typename T1, typename T2> inline bool chmax(T1 &a, T2 b) {
  return (a < b && (a = b, true));
}
template <typename T> bool isin(T y, T x, T h, T w) {
  return (0 <= y && 0 <= x && y < h && x < w);
}
template <typename T> bool isin1(T y, T x, T h, T w) {
  return (0 < y && 0 < x && y <= h && x <= w);
}

template <typename T> ostream &operator<<(ostream &os, vector<T> &v) {
  os << v[0];
  for (int i = 1; i < v.size(); i++)
    os << " " << v[i];
  return (os);
}

template <typename T> istream &operator>>(istream &is, vector<T> &v) {
  for (auto &u : v)
    is >> u;
  return (is);
}

template <typename T1, typename T2>
istream &operator>>(istream &is, pair<T1, T2> &p) {
  return (is >> p.first >> p.second);
}

void Main() {
  ll N, M;
  cin >> N >> M;
  vll S(N), T(M);
  cin >> S >> T;
  vvll dp(N + 1, vll(M + 1, 0));
  dp[0][0] = 1;
  for (int i = 0; i < N; i++) {
    for (int j = 0; j <= M; j++) {
      if (j < M && S[i] == T[j])
        (dp[i + 1][j + 1] += dp[i][j]) %= mod;
      if (i < N)
        (dp[i + 1][j] += dp[i][j]) %= mod;
      if (j < M)
        (dp[i][j + 1] += dp[i][j]) %= mod;
      if (i < N && j < M)
        (dp[i + 1][j + 1] += mod - dp[i][j]) %= mod;
    }
  }
  ll sum = 0;
  for (int i = 0; i <= M; i++) {
    (sum += dp[N][i]) %= mod;
  }
  cout << sum << endl;
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(0);
  cout << fixed << setprecision(20);
  Main();
  return (0);
}