Problem p02668 (C++) — buggy submission, verdict: Runtime Error

#pragma GCC optimize("O3")
#pragma GCC target("sse4")

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef long double ld;
typedef complex<ld> cd;

typedef pair<int, int> pi;
typedef pair<ll, ll> pl;
typedef pair<ld, ld> pd;

typedef vector<int> vi;
typedef vector<ld> vd;
typedef vector<ll> vl;
typedef vector<pi> vpi;
typedef vector<pl> vpl;
typedef vector<cd> vcd;

#define FOR(i, a, b) for (int i = a; i < (b); i++)
#define F0R(i, a) for (int i = 0; i < (a); i++)
#define FORd(i, a, b) for (int i = (b)-1; i >= a; i--)
#define F0Rd(i, a) for (int i = (a)-1; i >= 0; i--)

#define sz(x) (int)(x).size()
#define mp make_pair
#define pb push_back
#define f first
#define s second
#define lb lower_bound
#define ub upper_bound
#define all(x) x.begin(), x.end()
#define ins insert

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

const int MOD = 1000000007;
const char nl = '\\n';
const int MX = 100001; // check the limits, dummy

struct mi {
  ll v;
  explicit operator ll() const { return v; }
  mi() { v = 0; }
  mi(ll _v) {
    v = (-MOD < _v && _v < MOD) ? _v : _v % MOD;
    if (v < 0)
      v += MOD;
  }
  friend bool operator==(const mi &a, const mi &b) { return a.v == b.v; }
  friend bool operator!=(const mi &a, const mi &b) { return !(a == b); }
  friend bool operator<(const mi &a, const mi &b) { return a.v < b.v; }

  mi &operator+=(const mi &m) {
    if ((v += m.v) >= MOD)
      v -= MOD;
    return *this;
  }
  mi &operator-=(const mi &m) {
    if ((v -= m.v) < 0)
      v += MOD;
    return *this;
  }
  mi &operator*=(const mi &m) {
    v = v * m.v % MOD;
    return *this;
  }
  mi &operator/=(const mi &m) { return (*this) *= inv(m); }
  friend mi pow(mi a, ll p) {
    mi ans = 1;
    assert(p >= 0);
    for (; p; p /= 2, a *= a)
      if (p & 1)
        ans *= a;
    return ans;
  }
  friend mi inv(const mi &a) {
    assert(a.v != 0);
    return pow(a, MOD - 2);
  }

  mi operator-() const { return mi(-v); }
  mi &operator++() { return *this += 1; }
  mi &operator--() { return *this -= 1; }
  friend mi operator+(mi a, const mi &b) { return a += b; }
  friend mi operator-(mi a, const mi &b) { return a -= b; }
  friend mi operator*(mi a, const mi &b) { return a *= b; }
  friend mi operator/(mi a, const mi &b) { return a /= b; }
  friend ostream &operator<<(ostream &os, const mi &m) {
    os << m.v;
    return os;
  }
  friend istream &operator>>(istream &is, mi &m) {
    ll x;
    is >> x;
    m.v = x;
    return is;
  }
};

typedef vector<mi> vmi;
typedef pair<mi, mi> pmi;
typedef vector<pmi> vpmi;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  int M, N;
  cin >> M >> N;
  /*    mi cnt[N+1][N+1];
      F0R(i, N+1) {
          F0R(j, N+1) {
              cnt[i][j] = 0;
          }
          cnt[i][i] = i+1;
          FOR(j, 1, i) {
              mi lenVar = i - j - 1;
              mi curCnt = i - j + 1;
              cnt[i][j] = curCnt * pow((mi) 2, (ll) lenVar);
          }
      }*/

  mi dp[M + 1][N + 1];
  F0R(i, M + 1) F0R(j, N + 1) dp[i][j] = 0;
  dp[M][N] = 1;

  FORd(i, 1, M + 1) {
    mi cur = 0;
    mi sum = 0;
    FORd(j, 1, N + 1) {
      cur -= sum;
      cur *= 2;
      sum *= 2;
      if (j < N) {
        cur -= dp[i][j + 1] * (j + 2);
        sum -= dp[i][j + 1];
      }
      cur += (j + 1) * dp[i][j];
      sum += dp[i][j];
      dp[i - 1][j] = cur;
    }
  }

  mi ans = 0;
  FOR(i, 1, N + 1) ans += dp[0][i];
  cout << ans << nl;
  return 0;
}

// read the question correctly (ll vs int)
// template by bqi343


Error: 0

Fixed submission:

#pragma GCC optimize("O3")
#pragma GCC target("sse4")

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef long double ld;
typedef complex<ld> cd;

typedef pair<int, int> pi;
typedef pair<ll, ll> pl;
typedef pair<ld, ld> pd;

typedef vector<int> vi;
typedef vector<ld> vd;
typedef vector<ll> vl;
typedef vector<pi> vpi;
typedef vector<pl> vpl;
typedef vector<cd> vcd;

#define FOR(i, a, b) for (int i = a; i < (b); i++)
#define F0R(i, a) for (int i = 0; i < (a); i++)
#define FORd(i, a, b) for (int i = (b)-1; i >= a; i--)
#define F0Rd(i, a) for (int i = (a)-1; i >= 0; i--)

#define sz(x) (int)(x).size()
#define mp make_pair
#define pb push_back
#define f first
#define s second
#define lb lower_bound
#define ub upper_bound
#define all(x) x.begin(), x.end()
#define ins insert

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

const int MOD = 1000000007;
const char nl = '\\n';
const int MX = 100001; // check the limits, dummy

struct mi {
  ll v;
  explicit operator ll() const { return v; }
  mi() { v = 0; }
  mi(ll _v) {
    v = (-MOD < _v && _v < MOD) ? _v : _v % MOD;
    if (v < 0)
      v += MOD;
  }
  friend bool operator==(const mi &a, const mi &b) { return a.v == b.v; }
  friend bool operator!=(const mi &a, const mi &b) { return !(a == b); }
  friend bool operator<(const mi &a, const mi &b) { return a.v < b.v; }

  mi &operator+=(const mi &m) {
    if ((v += m.v) >= MOD)
      v -= MOD;
    return *this;
  }
  mi &operator-=(const mi &m) {
    if ((v -= m.v) < 0)
      v += MOD;
    return *this;
  }
  mi &operator*=(const mi &m) {
    v = v * m.v % MOD;
    return *this;
  }
  mi &operator/=(const mi &m) { return (*this) *= inv(m); }
  friend mi pow(mi a, ll p) {
    mi ans = 1;
    assert(p >= 0);
    for (; p; p /= 2, a *= a)
      if (p & 1)
        ans *= a;
    return ans;
  }
  friend mi inv(const mi &a) {
    assert(a.v != 0);
    return pow(a, MOD - 2);
  }

  mi operator-() const { return mi(-v); }
  mi &operator++() { return *this += 1; }
  mi &operator--() { return *this -= 1; }
  friend mi operator+(mi a, const mi &b) { return a += b; }
  friend mi operator-(mi a, const mi &b) { return a -= b; }
  friend mi operator*(mi a, const mi &b) { return a *= b; }
  friend mi operator/(mi a, const mi &b) { return a /= b; }
  friend ostream &operator<<(ostream &os, const mi &m) {
    os << m.v;
    return os;
  }
  friend istream &operator>>(istream &is, mi &m) {
    ll x;
    is >> x;
    m.v = x;
    return is;
  }
};

typedef vector<mi> vmi;
typedef pair<mi, mi> pmi;
typedef vector<pmi> vpmi;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  int M, N;
  cin >> M >> N;
  mi cnt[N + 1][N + 1];
  F0R(i, N + 1) {
    F0R(j, N + 1) { cnt[i][j] = 0; }
    cnt[i][i] = i + 1;
    FOR(j, 1, i) {
      mi lenVar = i - j - 1;
      mi curCnt = i - j + 1;
      cnt[i][j] = curCnt * pow((mi)2, (ll)lenVar);
    }
  }

  mi dp[M + 1][N + 1];
  F0R(i, M + 1) F0R(j, N + 1) dp[i][j] = 0;
  dp[M][N] = 1;

  FORd(i, 1, M + 1) {
    mi cur = 0;
    mi sum = 0;
    FORd(j, 1, N + 1) {
      cur -= sum;
      cur *= 2;
      sum *= 2;
      if (j < N) {
        cur -= (j + 2) * dp[i][j + 1];
        sum -= dp[i][j + 1];
      }
      cur += (j + 1) * dp[i][j];
      sum += dp[i][j];
      dp[i - 1][j] = cur;
    }
  }

  mi ans = 0;
  FOR(i, 1, N + 1) ans += dp[0][i];
  cout << ans << nl;
  return 0;
}

// read the question correctly (ll vs int)
// template by bqi343