Problem p02588 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;
///////////////////////////////////////////
const long long int INF = 1LL << 60;
const long long int Mod = 1000000007;
using ll = long long int;
using ci = const int;
using vi = vector<int>;
using Vi = vector<long long int>;
using P = pair<int, int>;
using PLL = pair<ll, ll>;
using matrix = vector<vector<ll>>;
#define pb(x) push_back(x)
#define mp(x, y) make_pair(x, y)
#define all(x) (x).begin(), (x).end()
#define rp(i, N) for (ll i = 0; i < (ll)N; i++)
#define repi(i, a, b) for (ll i = ll(a); i < ll(b); ++i)
template <class T> bool chmax(T &former, const T &b) {
  if (former < b) {
    former = b;
    return true;
  }
  return false;
}
template <class T> bool chmin(T &former, const T &b) {
  if (b < former) {
    former = b;
    return true;
  }
  return false;
}
template <class T> T sqar(T x) { return x * x; } // sqrt(x)は平方根;
#define Sort(v)                                                                \
  std::sort(v.begin(), v.end(),                                                \
            std::greater<decltype(v[0])>()) // 降順でVをソート
#define p_queue(v) priority_queue<v, vector<v>, greater<v>>
template <class T> inline void princ(T x) { cout << x << " "; };
template <class T> inline void print(T x) { cout << x << "\n"; };
template <class T> inline void Yes(T condition) {
  if (condition)
    cout << "Yes" << endl;
  else
    cout << "No" << endl;
}
template <class T> inline void YES(T condition) {
  if (condition)
    cout << "YES" << endl;
  else
    cout << "NO" << endl;
}
///////////////////////////////////////////////////////////////////////////////////

void solve() {
  ll n;
  cin >> n;
  Vi a(n);
  rp(i, n) {
    string s;
    cin >> s;
    int si = s.size();
    bool point = false;
    int num = 0;
    rp(j, si) {
      if (s[j] == '.') {
        point = true;
        num = si - j - 1;
        continue;
      }
      if (point) {
        s[j - 1] = s[j];
      }
    }
    if (point)
      s[si - 1] = '0';
    ll aa = stoll(s);
    if (!point)
      aa *= 1000000000;
    else {
      rp(j, 9 - num - 1) aa *= 10;
      if (num == 9)
        aa /= 10;
    }
    a[i] = aa;
  }
  matrix mat(19, Vi(19, 0)), summat(19, Vi(19, 0));
  rp(i, n) {
    ll t = 0, f = 0;
    ll as = a[i];
    while (as % 2 == 0) {
      as /= 2;
      t++;
    }
    while (as % 5 == 0) {
      as /= 5;
      f++;
    }
    mat[t][f]++;
  }
  for (ll i = 18; i >= 0; i--) {
    for (ll j = 18; j >= 0; j--) {
      if (i == 18 && j == 18) {
        summat[i][j] = mat[i][j];
        continue;
      }
      if (i == 18) {
        summat[i][j] = summat[i][j + 1] + mat[i][j];
        continue;
      }
      if (j == 18) {
        summat[i][j] = summat[i + 1][j] + mat[i][j];
        continue;
      }
      summat[i][j] = summat[i + 1][j] + summat[i][j + 1] -
                     summat[i + 1][j + 1] + mat[i][j];
    }
  }
  ll ans = 0;
  rp(i, 19) {
    rp(j, 19) {
      if (i >= 9 && j >= 9) {
        ans += mat[i][j] * (summat[18 - i][18 - j] - 1);
        continue;
      }
      ans += mat[i][j] * summat[18 - i][18 - j];
    }
  }
  ans /= 2;
  print(ans);
  return;
}
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  std::cout << std::fixed << std::setprecision(30);
  solve();
  return 0;
}

Fixed submission:
#include <bits/stdc++.h>
using namespace std;
///////////////////////////////////////////
const long long int INF = 1LL << 60;
const long long int Mod = 1000000007;
using ll = long long int;
using ci = const int;
using vi = vector<int>;
using Vi = vector<long long int>;
using P = pair<int, int>;
using PLL = pair<ll, ll>;
using matrix = vector<vector<ll>>;
#define pb(x) push_back(x)
#define mp(x, y) make_pair(x, y)
#define all(x) (x).begin(), (x).end()
#define rp(i, N) for (ll i = 0; i < (ll)N; i++)
#define repi(i, a, b) for (ll i = ll(a); i < ll(b); ++i)
template <class T> bool chmax(T &former, const T &b) {
  if (former < b) {
    former = b;
    return true;
  }
  return false;
}
template <class T> bool chmin(T &former, const T &b) {
  if (b < former) {
    former = b;
    return true;
  }
  return false;
}
template <class T> T sqar(T x) { return x * x; } // sqrt(x)は平方根;
#define Sort(v)                                                                \
  std::sort(v.begin(), v.end(),                                                \
            std::greater<decltype(v[0])>()) // 降順でVをソート
#define p_queue(v) priority_queue<v, vector<v>, greater<v>>
template <class T> inline void princ(T x) { cout << x << " "; };
template <class T> inline void print(T x) { cout << x << "\n"; };
template <class T> inline void Yes(T condition) {
  if (condition)
    cout << "Yes" << endl;
  else
    cout << "No" << endl;
}
template <class T> inline void YES(T condition) {
  if (condition)
    cout << "YES" << endl;
  else
    cout << "NO" << endl;
}
///////////////////////////////////////////////////////////////////////////////////

void solve() {
  ll n;
  cin >> n;
  Vi a(n);
  rp(i, n) {
    string s;
    cin >> s;
    int si = s.size();
    bool point = false;
    int num = 0;
    rp(j, si) {
      if (s[j] == '.') {
        point = true;
        num = si - j - 1;
        continue;
      }
      if (point) {
        s[j - 1] = s[j];
      }
    }
    if (point)
      s[si - 1] = '0';
    ll aa = stoll(s);
    if (!point)
      aa *= 1000000000;
    else {
      rp(j, 9 - num - 1) aa *= 10;
      if (num == 9)
        aa /= 10;
    }
    a[i] = aa;
  }
  matrix mat(19, Vi(19, 0)), summat(19, Vi(19, 0));
  rp(i, n) {
    ll t = 0, f = 0;
    ll as = a[i];
    while (as % 2 == 0) {
      as /= 2;
      t++;
    }
    while (as % 5 == 0) {
      as /= 5;
      f++;
    }
    if (t > 18)
      t = 18;
    if (f > 18)
      f = 18;
    mat[t][f]++;
  }
  for (ll i = 18; i >= 0; i--) {
    for (ll j = 18; j >= 0; j--) {
      if (i == 18 && j == 18) {
        summat[i][j] = mat[i][j];
        continue;
      }
      if (i == 18) {
        summat[i][j] = summat[i][j + 1] + mat[i][j];
        continue;
      }
      if (j == 18) {
        summat[i][j] = summat[i + 1][j] + mat[i][j];
        continue;
      }
      summat[i][j] = summat[i + 1][j] + summat[i][j + 1] -
                     summat[i + 1][j + 1] + mat[i][j];
    }
  }
  ll ans = 0;
  rp(i, 19) {
    rp(j, 19) {
      if (i >= 9 && j >= 9) {
        ans += mat[i][j] * (summat[18 - i][18 - j] - 1);
        continue;
      }
      ans += mat[i][j] * summat[18 - i][18 - j];
    }
  }
  ans /= 2;
  print(ans);
  return;
}
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  std::cout << std::fixed << std::setprecision(30);
  solve();
  return 0;
}