Problem p02757 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
#define endl "\n"
using namespace std;
#define ll long long
#define ld long double
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define repo(i, n) for (int i = 1; i < (int)(n); i++)
#define pb push_back
#define mp make_pair
#define np next_permutation
#define fi first
#define se second
#define all(x) (x).begin(), (x).end()
#define uniq(v) v.erase(unique(v.begin(), v.end()), v.end())
#define lb(v, x) (lower_bound(v.begin(), v.end(), x) - v.begin())
#define ub(v, x) (upper_bound(v.begin(), v.end(), x) - v.begin())
const ll mod = 1000000007;
// const ll mod=998244353;
const ld pi = acos(-1.0);
const ll INF = 1LL << 61;
template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}
ll gcd(ll x, ll y) { return y ? gcd(y, x % y) : x; }
ll lcm(ll x, ll y) { return x / gcd(x, y) * y; }
ll jou(ll N, ll P) {
  if (P == 0)
    return 1;
  if (P % 2 == 0) {
    ll t = jou(N, P / 2);
    return t * t % mod;
  }
  return (N * jou(N, P - 1)) % mod;
} // jou(n,mod-2)で逆元
// intの最大値2147483647 ≒ 2×10^9
// long longの最大値9223372036854775807 ≒ 9×10^18
//'大文字'+=32;    で小文字に
//   cout << fixed << setprecision (20);   小数点以下2０桁まで
// 実行時間制約2秒では２×10^8回くらいまで計算できる

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  int n, p;
  string s;
  cin >> n >> p >> s;

  ll ans = 0;

  if (p == 2) {
    rep(i, n) {
      if ((s[i] - '0') % 2 == 0)
        ans += i + 1;
    }
    cout << ans << endl;
    return 0;
  }
  if (p == 5) {
    rep(i, n) {
      if ((s[i] - '0') % 5 == 0)
        ans += i + 1;
    }
    cout << ans << endl;
    return 0;
  }

  vector<ll> q(p);
  q[0] = 1;
  ll now = 0;
  ll ju = 1;
  for (int i = n - 1; i >= 0; i--) {
    now += ((s[i] - '0') * ju);
    now %= p;
    q[now]++;
    ju = (ju * 10) % p;
  }

  rep(i, n) { ans += q[i] * (q[i] - 1) / 2; }

  cout << ans << endl;
}


Fixed submission:
#include <bits/stdc++.h>
#define endl "\n"
using namespace std;
#define ll long long
#define ld long double
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define repo(i, n) for (int i = 1; i < (int)(n); i++)
#define pb push_back
#define mp make_pair
#define np next_permutation
#define fi first
#define se second
#define all(x) (x).begin(), (x).end()
#define uniq(v) v.erase(unique(v.begin(), v.end()), v.end())
#define lb(v, x) (lower_bound(v.begin(), v.end(), x) - v.begin())
#define ub(v, x) (upper_bound(v.begin(), v.end(), x) - v.begin())
const ll mod = 1000000007;
// const ll mod=998244353;
const ld pi = acos(-1.0);
const ll INF = 1LL << 61;
template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}
ll gcd(ll x, ll y) { return y ? gcd(y, x % y) : x; }
ll lcm(ll x, ll y) { return x / gcd(x, y) * y; }
ll jou(ll N, ll P) {
  if (P == 0)
    return 1;
  if (P % 2 == 0) {
    ll t = jou(N, P / 2);
    return t * t % mod;
  }
  return (N * jou(N, P - 1)) % mod;
} // jou(n,mod-2)で逆元
// intの最大値2147483647 ≒ 2×10^9
// long longの最大値9223372036854775807 ≒ 9×10^18
//'大文字'+=32;    で小文字に
//   cout << fixed << setprecision (20);   小数点以下2０桁まで
// 実行時間制約2秒では２×10^8回くらいまで計算できる

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  int n, p;
  string s;
  cin >> n >> p >> s;

  ll ans = 0;

  if (p == 2) {
    rep(i, n) {
      if ((s[i] - '0') % 2 == 0)
        ans += i + 1;
    }
    cout << ans << endl;
    return 0;
  }
  if (p == 5) {
    rep(i, n) {
      if ((s[i] - '0') % 5 == 0)
        ans += i + 1;
    }
    cout << ans << endl;
    return 0;
  }

  vector<ll> q(p);
  q[0] = 1;
  ll now = 0;
  ll ju = 1;
  for (int i = n - 1; i >= 0; i--) {
    now += ((s[i] - '0') * ju);
    now %= p;
    q[now]++;
    ju = (ju * 10) % p;
  }

  rep(i, p) { ans += q[i] * (q[i] - 1) / 2; }

  cout << ans << endl;
}