multof2019

other/multof2019/multof2019.cpp

@@ -0,0 +1,30 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+#define MAX_N 200000
+#define ll long long
+
+vector<int> cnt(2019, 0);
+
+int main()
+{
+  string s;
+  cin >> s;
+
+  int num = 0, power = 1;
+  cnt[0] = 1;
+  for (int i = s.size() - 1; i >= 0; --i)
+  {
+    num = (num + power * (s[i] - '0')) % 2019;
+    ++cnt[num];
+    power = (power * 10) % 2019;
+  }
+
+  ll ans = 0;
+  for (int i = 0; i < 2019; ++i)
+    ans += static_cast<ll>(cnt[i]) * (cnt[i] - 1) / 2;
+
+  cout << ans << '\n';
+
+  return 0;  
+}