Problem p02653 (C++) — buggy submission, verdict: Runtime Error

#include <bits/stdc++.h>
// ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
// clock_t start=clock();clock_t
// end=clock();cout<<(double)(end-start)/CLOCKS_PER_SEC<<endl;
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef unsigned int ui;
typedef pair<int, int> pii;
typedef pair<pii, int> ppii;
typedef pair<int, pii> pipi;
typedef pair<ll, ll> pll;
typedef pair<pll, ll> ppll;
typedef pair<ll, pll> plpl;
typedef pair<pii, pii> pippi;
typedef tuple<ll, ll, ll> tl;
typedef pair<double, double> pdd;
typedef vector<vector<ll>> mat;
ll mod = 1000000007;
ll mod2 = 998244353;
ll mod3 = 1000003;
ll mod4 = 998244853;
ll mod5 = 1000000009;
ll inf = 1LL << 62;
int iinf = 1 << 30;
double pi = 3.141592653589793238462643383279L;
double eps = 1e-8;
#define rep(i, m, n) for (int i = m; i < n; i++)
#define rrep(i, n, m) for (ll i = n; i >= m; i--)
#define srep(itr, st) for (auto itr = st.begin(); itr != st.end(); itr++)
#define mrep(itr, mp) for (auto &itr : mp)
#define Max(a, b) a = max(a, b)
#define Min(a, b) a = min(a, b)
// #define endl "\\n"
int dh[4] = {1, -1, 0, 0};
int dw[4] = {0, 0, 1, -1};
int ddh[8] = {-1, -1, -1, 0, 0, 1, 1, 1};
int ddw[8] = {-1, 0, 1, -1, 1, -1, 0, 1};
struct custom_hash {
  static uint64_t splitmix64(uint64_t x) {
    // http://xorshift.di.unimi.it/splitmix64.c
    x += 0x9e3779b97f4a7c15;
    x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
    x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
    return x ^ (x >> 31);
  }

  size_t operator()(uint64_t x) const {
    static const uint64_t FIXED_RANDOM =
        chrono::steady_clock::now().time_since_epoch().count();
    return splitmix64(x + FIXED_RANDOM);
  }
};
#define umh unordered_map<int, int, custom_hash>
ll gcd(ll a, ll b) {
  if (a < b)
    swap(a, b);
  if (b == 0)
    return a;
  if (a % b == 0)
    return b;
  return gcd(b, a % b);
}
ll lcm(ll a, ll b) {
  ll c = gcd(a, b);
  return a * b / c;
}
ll Pow(ll n, ll k) {
  if (k < 0)
    return 0;
  ll ret = 1;
  ll now = n;
  while (k > 0) {
    if (k & 1)
      ret *= now;
    now *= now;
    k /= 2;
  }
  return ret;
}
ll beki(ll n, ll k, ll md) {
  ll ret = 1;
  ll now = n;
  now %= md;
  while (k > 0) {
    if (k % 2 == 1) {
      ret *= now;
      ret %= md;
    }
    now *= now;
    now %= md;
    k /= 2;
  }
  return ret;
}
ll gyaku(ll n, ll md) { return beki(n, md - 2, md); }
ll popcount(ll n) {
  ll ret = 0;
  ll u = n;
  while (u > 0) {
    ret += u % 2;
    u /= 2;
  }
  return ret;
}

ll dp[5010][5010];
ll sum1[5010];
ll sum2[5010][5010];
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  ll n, a[2];
  cin >> n >> a[0] >> a[1];
  if (a[0] < a[1])
    swap(a[0], a[1]);
  memset(dp, 0, sizeof dp);
  dp[0][0] = 1;
  memset(sum1, 0, sizeof sum1);
  sum1[0] = 1;
  memset(sum2, 0, sizeof sum2);
  sum2[0][0] = 1;
  rep(i, 1, n + 1) {
    rep(j, 1, a[0]) {
      if (j == 1) {
        ll le = max(i - a[1], (ll)0);
        if (i == 1) {
          dp[i][j] = 1;
        } else {
          if (le == 0)
            dp[i][j] = sum1[i - 2];
          else
            dp[i][j] = (sum1[i - 2] - sum1[le - 1] + mod) % mod;
        }
      } else if (j <= a[1]) {
        dp[i][j] = dp[i - 1][j - 1];
      } else {
        if (i < j)
          continue;
        dp[i][j] = (sum2[i - j][i - (a[1] + 1)] + dp[i - 1][j - 1]) % mod;
      }
    }
    sum1[i] = sum1[i - 1];
    rep(j, 1, min(a[0], (ll)i + 1)) {
      (sum1[i] += dp[i][j]) %= mod;
      sum2[i - j][i] = (sum2[i - j][i - 1] + dp[i][j]) % mod;
    }
  }
  ll ans = beki(2, n, mod);
  ll sum = 0;
  rep(i, 0, n + 1) {
    rep(j, 0, n + 1) {
      ll noko = n - i;
      if (noko < a[1])
        noko = 0;
      if (j + noko < a[0]) {
        (sum += dp[i][j]) %= mod;
      }
    }
  }
  ans = ans - sum + mod;
  cout << ans % mod << endl;
}


Error: 0

Fixed submission:

#include <bits/stdc++.h>
// ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
// clock_t start=clock();clock_t
// end=clock();cout<<(double)(end-start)/CLOCKS_PER_SEC<<endl;
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef unsigned int ui;
typedef pair<int, int> pii;
typedef pair<pii, int> ppii;
typedef pair<int, pii> pipi;
typedef pair<ll, ll> pll;
typedef pair<pll, ll> ppll;
typedef pair<ll, pll> plpl;
typedef pair<pii, pii> pippi;
typedef tuple<ll, ll, ll> tl;
typedef pair<double, double> pdd;
typedef vector<vector<ll>> mat;
ll mod = 1000000007;
ll mod2 = 998244353;
ll mod3 = 1000003;
ll mod4 = 998244853;
ll mod5 = 1000000009;
ll inf = 1LL << 62;
int iinf = 1 << 30;
double pi = 3.141592653589793238462643383279L;
double eps = 1e-8;
#define rep(i, m, n) for (int i = m; i < n; i++)
#define rrep(i, n, m) for (ll i = n; i >= m; i--)
#define srep(itr, st) for (auto itr = st.begin(); itr != st.end(); itr++)
#define mrep(itr, mp) for (auto &itr : mp)
#define Max(a, b) a = max(a, b)
#define Min(a, b) a = min(a, b)
// #define endl "\\n"
int dh[4] = {1, -1, 0, 0};
int dw[4] = {0, 0, 1, -1};
int ddh[8] = {-1, -1, -1, 0, 0, 1, 1, 1};
int ddw[8] = {-1, 0, 1, -1, 1, -1, 0, 1};
struct custom_hash {
  static uint64_t splitmix64(uint64_t x) {
    // http://xorshift.di.unimi.it/splitmix64.c
    x += 0x9e3779b97f4a7c15;
    x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
    x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
    return x ^ (x >> 31);
  }

  size_t operator()(uint64_t x) const {
    static const uint64_t FIXED_RANDOM =
        chrono::steady_clock::now().time_since_epoch().count();
    return splitmix64(x + FIXED_RANDOM);
  }
};
#define umh unordered_map<int, int, custom_hash>
ll gcd(ll a, ll b) {
  if (a < b)
    swap(a, b);
  if (b == 0)
    return a;
  if (a % b == 0)
    return b;
  return gcd(b, a % b);
}
ll lcm(ll a, ll b) {
  ll c = gcd(a, b);
  return a * b / c;
}
ll Pow(ll n, ll k) {
  if (k < 0)
    return 0;
  ll ret = 1;
  ll now = n;
  while (k > 0) {
    if (k & 1)
      ret *= now;
    now *= now;
    k /= 2;
  }
  return ret;
}
ll beki(ll n, ll k, ll md) {
  ll ret = 1;
  ll now = n;
  now %= md;
  while (k > 0) {
    if (k % 2 == 1) {
      ret *= now;
      ret %= md;
    }
    now *= now;
    now %= md;
    k /= 2;
  }
  return ret;
}
ll gyaku(ll n, ll md) { return beki(n, md - 2, md); }
ll popcount(ll n) {
  ll ret = 0;
  ll u = n;
  while (u > 0) {
    ret += u % 2;
    u /= 2;
  }
  return ret;
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  ll n, a[2];
  cin >> n >> a[0] >> a[1];
  if (a[0] < a[1])
    swap(a[0], a[1]);
  ll dp[n + 1][n + 1];
  memset(dp, 0, sizeof dp);
  dp[0][0] = 1;
  ll sum1[n + 1];
  memset(sum1, 0, sizeof sum1);
  sum1[0] = 1;
  ll sum2[n + 1][n + 1];
  memset(sum2, 0, sizeof sum2);
  sum2[0][0] = 1;
  rep(i, 1, n + 1) {
    rep(j, 1, a[0]) {
      if (j == 1) {
        ll le = max(i - a[1], (ll)0);
        if (i == 1) {
          dp[i][j] = 1;
        } else {
          if (le == 0)
            dp[i][j] = sum1[i - 2];
          else
            dp[i][j] = (sum1[i - 2] - sum1[le - 1] + mod) % mod;
        }
      } else if (j <= a[1]) {
        dp[i][j] = dp[i - 1][j - 1];
      } else {
        if (i < j)
          continue;
        dp[i][j] = (sum2[i - j][i - (a[1] + 1)] + dp[i - 1][j - 1]) % mod;
      }
    }
    sum1[i] = sum1[i - 1];
    rep(j, 1, min(a[0], (ll)i + 1)) {
      (sum1[i] += dp[i][j]) %= mod;
      sum2[i - j][i] = (sum2[i - j][i - 1] + dp[i][j]) % mod;
    }
  }
  ll ans = beki(2, n, mod);
  ll sum = 0;
  rep(i, 0, n + 1) {
    rep(j, 0, n + 1) {
      ll noko = n - i;
      if (noko < a[1])
        noko = 0;
      if (j + noko < a[0]) {
        (sum += dp[i][j]) %= mod;
      }
    }
  }
  ans = ans - sum + mod;
  cout << ans % mod << endl;
}