C - Chat Ban

https://codeforces.com/contest/1612/submission/136476673

CodeForces/1612/C/C.cpp

@@ -0,0 +1,49 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+int t, k;
+long long x, ans;
+
+inline long long calc(long long d) {
+    return (d + 1) * d / 2;
+}
+
+inline long long calc2(long long d) {
+    return (k * 2 - d + 1) * d / 2;
+}
+
+int main() {
+    cin >> t;
+    while (t--) {
+        cin >> k >> x;
+        long long l = 0, r = k;
+        while (l < r) {
+            int mid = l + r + 1 >> 1;
+            if (calc(mid) <= x) {
+                l = mid;
+            } else {
+                r = mid - 1;
+            }
+        }
+        if (r < k) {
+            ans = r + (calc(r) < x);
+            cout << min(ans, k * 2ll - 1) << endl;
+            continue;
+        }
+        x -= (k - 1ll) * k / 2ll;
+        l = 0;
+        r = k;
+        while (l < r) {
+            int mid = l + r + 1 >> 1;
+            if (calc2(mid) <= x) {
+                l = mid;
+            } else {
+                r = mid - 1;
+            }
+        }
+        ans = (r + k - 1 + (calc2(r) < x));
+        cout << min(ans, k * 2ll - 1) << endl;
+    }
+    return 0;
+}