Problem p00994 (C++) — buggy submission, verdict: Runtime Error

#include "bits/stdc++.h"
using namespace std;

const int mod = 100000007;
struct Mod {
public:
  int num;
  Mod() : Mod(0) { ; }
  Mod(long long int n) : num((n % mod + mod) % mod) {
    static_assert(mod < INT_MAX / 2,
                  "mod is too big, please make num 'long long int' from 'int'");
  }
  Mod(int n) : Mod(static_cast<long long int>(n)) { ; }
  operator int() { return num; }
};

Mod operator+(const Mod a, const Mod b) { return Mod((a.num + b.num) % mod); }
Mod operator+(const long long int a, const Mod b) { return Mod(a) + b; }
Mod operator+(const Mod a, const long long int b) { return b + a; }
Mod operator++(Mod &a) { return a + Mod(1); }
Mod operator-(const Mod a, const Mod b) {
  return Mod((mod + a.num - b.num) % mod);
}
Mod operator-(const long long int a, const Mod b) { return Mod(a) - b; }
Mod operator--(Mod &a) { return a - Mod(1); }
Mod operator*(const Mod a, const Mod b) {
  return Mod(((long long)a.num * b.num) % mod);
}
Mod operator*(const long long int a, const Mod b) { return Mod(a) * b; }
Mod operator*(const Mod a, const long long int b) { return Mod(b) * a; }
Mod operator*(const Mod a, const int b) { return Mod(b) * a; }
Mod operator+=(Mod &a, const Mod b) { return a = a + b; }
Mod operator+=(long long int &a, const Mod b) { return a = a + b; }
Mod operator-=(Mod &a, const Mod b) { return a = a - b; }
Mod operator-=(long long int &a, const Mod b) { return a = a - b; }
Mod operator*=(Mod &a, const Mod b) { return a = a * b; }
Mod operator*=(long long int &a, const Mod b) { return a = a * b; }
Mod operator*=(Mod &a, const long long int &b) { return a = a * b; }
Mod operator^(const Mod a, const int n) {
  if (n == 0)
    return Mod(1);
  Mod res = (a * a) ^ (n / 2);
  if (n % 2)
    res = res * a;
  return res;
}
Mod mod_pow(const Mod a, const long long int n) {
  if (n == 0)
    return Mod(1);
  Mod res = mod_pow((a * a), (n / 2));
  if (n % 2)
    res = res * a;
  return res;
}
Mod inv(const Mod a) { return a ^ (mod - 2); }
Mod operator/(const Mod a, const Mod b) {
  assert(b.num != 0);
  return a * inv(b);
}
Mod operator/(const long long int a, const Mod b) { return Mod(a) / b; }
Mod operator/=(Mod &a, const Mod b) { return a = a / b; }

long long int getid(int x, int y, const vector<int> &v, int l) {
  long long int id = 0;
  id += x;
  id *= 15;
  id += y;
  for (int i = 0; i < v.size(); ++i) {
    assert(v[i] >= 0 && v[i] <= 2);
    id *= 31;
    id += v[i];
  }
  id *= 31;
  id += l;
  return id;
}
map<long long int, Mod> memo;
int R, C;
vector<vector<int>> field;
Mod getans(int x, int y, const vector<int> &v, int l) {
  assert(x < C);
  assert(R != y || !x);
  const long long int id = getid(x, y, v, l);
  if (memo.find(id) != memo.end()) {
    return memo[id];
  } else {
    if (y == R) {
      bool ok = true;
      if (l)
        ok = false;
      if (!all_of(v.begin(), v.end(), [](const int n) { return n == 0; }))
        ok = false;
      return memo[id] = ok;
    } else {
      if (x == 0) {
        if (l)
          return memo[id] = 0;
      }
      if (field[y][x]) {
        Mod ans = 0;
        for (int lnum = 0; lnum <= 2; lnum++) {
          int dnum = field[y][x] - l - v[x] - lnum;
          if (dnum < 0 || dnum >= 3)
            ans += 0;
          else {
            int nexty = y, nextx = x + 1;
            vector<int> nextv(v);
            if (nextx == C) {
              nextx = 0;
              nexty++;
            }
            nextv[x] = dnum;
            ans += getans(nextx, nexty, nextv, lnum);
          }
        }
        return memo[id] = ans;
      } else {
        if (l && v[x])
          return memo[id] = 0;
        else {
          int nexty = y, nextx = x + 1;
          vector<int> nextv(v);
          if (nextx == C) {
            nextx = 0;
            nexty++;
          }
          return memo[id] = getans(nextx, nexty, v, l);
        }
      }
    }
  }
  assert(false);
  return memo[id];
}
int main() {
  cin >> R >> C;
  field = vector<vector<int>>(R, vector<int>(C));
  for (int i = 0; i < R; ++i) {
    string st;
    cin >> st;
    for (int j = 0; j < C; ++j) {
      if (st[j] == '.')
        field[i][j] = 0;
      else
        field[i][j] = st[j] - '0';
    }
  }
  vector<int> v(C);
  Mod ans = getans(0, 0, v, 0);
  cout << ans << endl;
  return 0;
}

Error: -6
da3197f9-d85f-4b20-afc9-0e8bc58bc1e2.out: /home/alex/Documents/bug-detection/input/Project_CodeNet/data/p00994/C++/s965543419.cpp:79: Mod getans(int, int, const std::vector<int>&, int): Assertion `R != y || x' failed.


Fixed submission:

#include "bits/stdc++.h"
using namespace std;

const int mod = 100000007;
struct Mod {
public:
  int num;
  Mod() : Mod(0) { ; }
  Mod(long long int n) : num((n % mod + mod) % mod) {
    static_assert(mod < INT_MAX / 2,
                  "mod is too big, please make num 'long long int' from 'int'");
  }
  Mod(int n) : Mod(static_cast<long long int>(n)) { ; }
  operator int() { return num; }
};

Mod operator+(const Mod a, const Mod b) { return Mod((a.num + b.num) % mod); }
Mod operator+(const long long int a, const Mod b) { return Mod(a) + b; }
Mod operator+(const Mod a, const long long int b) { return b + a; }
Mod operator++(Mod &a) { return a + Mod(1); }
Mod operator-(const Mod a, const Mod b) {
  return Mod((mod + a.num - b.num) % mod);
}
Mod operator-(const long long int a, const Mod b) { return Mod(a) - b; }
Mod operator--(Mod &a) { return a - Mod(1); }
Mod operator*(const Mod a, const Mod b) {
  return Mod(((long long)a.num * b.num) % mod);
}
Mod operator*(const long long int a, const Mod b) { return Mod(a) * b; }
Mod operator*(const Mod a, const long long int b) { return Mod(b) * a; }
Mod operator*(const Mod a, const int b) { return Mod(b) * a; }
Mod operator+=(Mod &a, const Mod b) { return a = a + b; }
Mod operator+=(long long int &a, const Mod b) { return a = a + b; }
Mod operator-=(Mod &a, const Mod b) { return a = a - b; }
Mod operator-=(long long int &a, const Mod b) { return a = a - b; }
Mod operator*=(Mod &a, const Mod b) { return a = a * b; }
Mod operator*=(long long int &a, const Mod b) { return a = a * b; }
Mod operator*=(Mod &a, const long long int &b) { return a = a * b; }
Mod operator^(const Mod a, const int n) {
  if (n == 0)
    return Mod(1);
  Mod res = (a * a) ^ (n / 2);
  if (n % 2)
    res = res * a;
  return res;
}
Mod mod_pow(const Mod a, const long long int n) {
  if (n == 0)
    return Mod(1);
  Mod res = mod_pow((a * a), (n / 2));
  if (n % 2)
    res = res * a;
  return res;
}
Mod inv(const Mod a) { return a ^ (mod - 2); }
Mod operator/(const Mod a, const Mod b) {
  assert(b.num != 0);
  return a * inv(b);
}
Mod operator/(const long long int a, const Mod b) { return Mod(a) / b; }
Mod operator/=(Mod &a, const Mod b) { return a = a / b; }

long long int getid(int x, int y, const vector<int> &v, int l) {
  long long int id = 0;
  id += x;
  id *= 10;
  id += y;
  id *= 10;
  for (int i = 0; i < v.size(); ++i) {
    id += v[i];
    id *= 10;
  }
  id += l;
  return id;
}
map<long long int, Mod> memo;
int R, C;
vector<vector<int>> field;
Mod getans(int x, int y, const vector<int> &v, int l) {
  // assert(x < C);
  assert(R != y || x);
  const long long int id = getid(x, y, v, l);
  if (memo.find(id) != memo.end()) {
    return memo[id];
  } else {
    if (y == R) {
      bool ok = true;
      if (l)
        ok = false;
      if (!all_of(v.begin(), v.end(), [](const int n) { return n == 0; }))
        ok = false;
      return memo[id] = ok;
    } else {
      if (x == 0) {
        if (l)
          return memo[id] = 0;
      }
      if (field[y][x]) {
        Mod ans = 0;
        for (int lnum = 0; lnum <= 2; lnum++) {
          int dnum = field[y][x] - l - v[x] - lnum;
          if (dnum < 0 || dnum >= 3)
            ans += 0;
          else {
            int nexty = y, nextx = x + 1;
            vector<int> nextv(v);
            if (nextx == C) {
              nextx = 0;
              nexty++;
            }
            nextv[x] = dnum;
            ans += getans(nextx, nexty, nextv, lnum);
          }
        }
        return memo[id] = ans;
      } else {
        if (l && v[x])
          return memo[id] = 0;
        else {
          int nexty = y, nextx = x + 1;
          vector<int> nextv(v);
          if (nextx == C) {
            nextx = 0;
            nexty++;
          }
          return memo[id] = getans(nextx, nexty, v, l);
        }
      }
    }
  }
  assert(false);
  return memo[id];
}
int main() {
  cin >> R >> C;
  field = vector<vector<int>>(R, vector<int>(C));
  for (int i = 0; i < R; ++i) {
    string st;
    cin >> st;
    for (int j = 0; j < C; ++j) {
      if (st[j] == '.')
        field[i][j] = 0;
      else
        field[i][j] = st[j] - '0';
    }
  }
  vector<int> v(C);
  Mod ans = getans(0, 0, v, 0);
  cout << ans << endl;
  return 0;
}