more cf

cses/introductory-problems/digit-queries.cc

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+#include <bits/stdc++.h>  // {{{
+
+// https://codeforces.com/blog/entry/96344
+
+#pragma GCC optimize("O2,unroll-loops")
+#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
+
+using namespace std;
+
+template <typename T>
+constexpr T MIN = std::numeric_limits<T>::min();
+
+template <typename T>
+constexpr T MAX = std::numeric_limits<T>::max();
+
+template <typename T>
+[[nodiscard]] static T sc(auto&& x) {
+  return static_cast<T>(x);
+}
+
+template <typename T>
+[[nodiscard]] static T sz(auto&& x) {
+  return static_cast<T>(x.size());
+}
+
+using ll = long long;
+using ld = long double;
+template <typename T>
+using vec = std::vector<T>;
+template <typename T, size_t N>
+using arr = std::array<T, N>;
+
+#define ff first
+#define ss second
+#define eb emplace_back
+#define pb push_back
+#define all(x) (x).begin(), (x).end()
+#define rall(x) (x).rbegin(), (x).rend()
+//  }}}
+
+void solve() {
+  int q;
+  cin >> q;
+  while (q--) {
+    ll k;
+    cin >> k;
+    if (k <= 9) {
+      cout << k << endl;
+      continue;
+    }
+
+    ll exp = 1;
+    while (true) {
+      ll numbers_in_band = 9 * powl(10, exp - 1);
+      ll per = numbers_in_band * exp;
+
+      if (k <= per)
+        break;
+
+      k -= per;
+      exp++;
+    }
+
+    ll i = (k - 1) / exp;
+    ll index = k % exp;
+    if (index == 0)
+      index = exp;
+    ll ans = powl(10, exp - 1) + i;
+    ll offset = exp - index;
+    while (offset--) {
+      ans /= 10;
+    }
+
+    cout << ans % 10 << endl;
+  }
+}
+
+int main() {  // {{{
+  cin.tie(nullptr)->sync_with_stdio(false);
+
+  solve();
+
+  return 0;
+}
+// }}}