Language: C++

#include <iostream>
#include <iosfwd>
#include <iomanip>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <ctime>
#include <cmath>
#include <cassert>
#include <cctype>
#include <climits>
#include <vector>
#include <bitset>
#include <set>
#include <queue>
#include <stack>
#include <map>
#include <deque>
#include <string>
#include <list>
#include <iterator>
#include <sstream>
#include <complex>
#include <fstream>
#include <functional>
#include <numeric>
#include <utility>
#include <algorithm>

using namespace std;

// MACROS_BEGIN
#define CLEAR() cerr << endl;
#define LET(x, a) __typeof(a) x = a
#define FOREACH(it, v) for (LET(it, (v).begin()); it != (v).end(); ++it)
#define REPEAT(i, n) for (int i = 0; i < (n); ++i)
// MACROS_END

// GENERIC_UTILITIES_BEGIN
template <class T> inline int size(const T& c) {return (int) c.size();}
inline long long two(int x) {return (1LL << (x));}

vector<string> split(string s, string delim) {
    s += delim[0];
    string tmp;
    vector<string> result;
    for (int i = 0; i < size(s); ++i) {
        if (delim.find(s[i]) == string::npos) {
            tmp.push_back(s[i]);
        }
        else {
            if (tmp != "") result.push_back(tmp);
            tmp.clear();
        }
    }
    return result;
}

template <class A, class B> void setMin(A& a, const B& b) {
    a = min(a, b);
}

template <class A, class B> void setMax(A& a, const B& b) {
    a = max(a, b);
}
// GENERIC_UTILITIES_END

// FAST_IO_BEGIN
// FAST_IO_END

// STANDARD_IO_BEGIN
#ifndef USING_FAST_IO
int readInt() {int N = -1; scanf("%d", &N); return N;}
double readDouble() {double D; scanf("%lf", &D); return D;}
string readString() {char buffer[1 << 20]; scanf("%s", buffer); return buffer;}
long long readLongLong() {long long N = -1; scanf("%lld", &N); return N;}
#endif // NOT DEFINED USING_FAST_IO
// STANDARD_IO_END


// OUTPUT_UTILITIES_BEGIN
template <class A, class B> ostream& operator << (ostream& o, const pair<A, B>& p);
template <class T> ostream& operator << (ostream& o, const vector<T>& v);
template <class A, class B> ostream& operator << (ostream& o, const map<A, B>& m);
template <class T> ostream& operator << (ostream& o, const set<T>& s);
template <class T> ostream& operator << (ostream& o, const queue<T>& q);
template <class T> ostream& operator << (ostream& o, const stack<T>& s);

template <class A, class B> ostream& operator << (ostream& o, const pair<A, B>& p) {
    o << "(" << p.first << "," << p.second << ")"; return o;
}

template <class T> ostream& operator << (ostream& o, const vector<T>& v) {
    o << "{"; bool first = true; FOREACH(it, v) { if (!first) o << ","; first = false; o << *it; } return o << "}";
}

template <class A, class B> ostream& operator << (ostream& o, const map<A, B>& m) {
    o << "{"; bool first = true; FOREACH(it, m) { if (!first) o << ","; first = false; o << *it; } return o << "}";
}

template <class T> ostream& operator << (ostream& o, const set<T>& s) {
    o << "{"; bool first = true; FOREACH(it, s) { if (!first) o << ","; first = false; o << *it; } return o << "}";
}

template <class T> ostream& operator << (ostream& o, const queue<T>& q) {
    o << "{"; bool first = true; queue<T> p = q; while (!p.empty()) { if (!first) o << ","; first = false; o << p.front(); p.pop(); } return o << "}";
}

template <class T> ostream& operator << (ostream& o, const stack<T>& s) {
    o << "{"; bool first = true; stack<T> r = s; while (!r.empty()) { if (!first) o << ","; first = false; o << r.top(); r.pop(); } return o << "}";
}
// OUTPUT_UTILITIES_END

// DEBUGGING_UTILITIES_BEGIN
// DEBUGGING SWITCH
#define PHOENIX_DEBUG

#ifdef PHOENIX_DEBUG
#define BUG(x) cerr << __LINE__ << ": " << #x << " = " << x << endl;
#else
#define BUG(...)
#endif
// DEBUGGING_UTILITIES_END

const double epsilon = 1e-8;
const int infinite    = 1000000000;
const long long infiniteLL = 1000000000000000000LL;
const long long modulo = 1000000007;

struct Solver {
    int solve(string& s, int N) {
        vector<int> count(N, 0);
        count[0] = 1;
        int mult = 1;

        int result = 0;
        int prev = 0;

        for (int i = size(s) - 1; i >= 0; --i) {
            int digit = s[i] - '0';
            int currRemainder = ((digit * mult) + prev) % N;

            if (count[currRemainder] > 0) {
                result += count[currRemainder];
            }

            count[currRemainder]++;
            mult = (mult * 10) % N;
            prev = currRemainder;
        }

        return result;
    }
};

int main()
{
    string s = readString();
    Solver solver;
    int result = solver.solve(s, 2019);
    cout << result << endl;

    return 0;
}

// Powered by PhoenixAI


Compiler output:
a.cc: In function 'std::vector<std::__cxx11::basic_string<char> > split(std::string, std::string)':
a.cc:47:29: error: call of overloaded 'size(std::string&)' is ambiguous
   47 |     for (int i = 0; i < size(s); ++i) {
      |                         ~~~~^~~
a.cc:40:31: note: candidate: 'int size(const T&) [with T = std::__cxx11::basic_string<char>]'
   40 | template <class T> inline int size(const T& c) {return (int) c.size();}
      |                               ^~~~
In file included from /usr/include/c++/14/string:53,
                 from /usr/include/c++/14/bits/locale_classes.h:40,
                 from /usr/include/c++/14/bits/ios_base.h:41,
                 from /usr/include/c++/14/ios:44,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 from a.cc:1:
/usr/include/c++/14/bits/range_access.h:262:5: note: candidate: 'constexpr decltype (__cont.size()) std::size(const _Container&) [with _Container = __cxx11::basic_string<char>; decltype (__cont.size()) = long unsigned int]'
  262 |     size(const _Container& __cont) noexcept(noexcept(__cont.size()))
      |     ^~~~
a.cc: In member function 'int Solver::solve(std::string&, int)':
a.cc:139:26: error: call of overloaded 'size(std::string&)' is ambiguous
  139 |         for (int i = size(s) - 1; i >= 0; --i) {
      |                      ~~~~^~~
a.cc:40:31: note: candidate: 'int size(const T&) [with T = std::__cxx11::basic_string<char>]'
   40 | template <class T> inline int size(const T& c) {return (int) c.size();}
      |                               ^~~~
/usr/include/c++/14/bits/range_access.h:262:5: note: candidate: 'constexpr decltype (__cont.size()) std::size(const _Container&) [with _Container = __cxx11::basic_string<char>; decltype (__cont.size()) = long unsigned int]'
  262 |     size(const _Container& __cont) noexcept(noexcept(__cont.size()))
      |     ^~~~