done 3 sorting problems

CSES - CSES Problem Set/Introducotry_Problems/Digit_Queries.cpp

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+//  Digit Queries
+
+#include<bits/stdc++.h>
+
+using namespace std;
+using ll = long long;
+
+
+long long int power(ll base, ll exp)
+{
+    if (exp == 0)
+        return 1;
+    else if (exp == 1)
+        return base;
+    else
+    {
+        long long int calc;
+        if (exp % 2 == 0)
+        {
+            calc = power(base, exp/2);
+            calc *= calc;
+        }
+        else
+        {
+            calc = base*power(base, exp-1);
+        }
+        return calc;
+    }
+}
+
+
+int main() {
+    ll q; cin >> q;
+    for (ll _{}; _ < q; _++) {
+        ll k; cin >> k;
+        if (k < 10) {cout << k << endl; continue;}
+        ll number_length =  1;
+        ll highest_idx = 0;
+        while (highest_idx < k) {
+            highest_idx += number_length * 9 * power(10, number_length-1);
+            number_length++;
+        }
+        number_length--;
+        ll pos = k - highest_idx + number_length * 9 * power(10, number_length - 1) - 1;
+        ll number = pos / (number_length);
+        number += power(10, number_length - 1);
+//        cout << number << " " << number_length << endl;
+
+        ll decimal_pos = pos % number_length;
+        ll out = (number / (power(10, number_length - decimal_pos - 1))) % 10 ;
+        cout << out << endl;
+    }
+    return 0;
+}