P2261 [CQOI2007]余数求和

https://www.luogu.com.cn/record/76170293

Luogu/P2261/P2261.cpp

@@ -0,0 +1,29 @@
+#include <iostream>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+long long n, k, ans;
+
+int main() {
+    std::ios::sync_with_stdio(false);
+
+    cin >> n >> k;
+
+    ans = n * k;
+
+    for (long long l = 1, r; l <= n; l = r + 1) {
+        if (k / l) {
+            r = std::min(k / (k / l), n);
+        } else {
+            r = n;
+        }
+
+        ans -= (r + l) * (k / l) * (r - l + 1) / 2;
+    }
+
+    cout << ans << endl;
+
+    return 0;
+}