B3969 [GESP202403 五级] B-smooth 数

https://www.luogu.com.cn/record/174743452

Luogu/B3969/B3969.cpp

@@ -0,0 +1,34 @@
+#include <iostream>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 1e6 + 5;
+
+int n, b, a[N]{0, 1}, cnt;
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n >> b;
+
+    for (int i = 2; i <= n; i++) {
+        if (a[i] == 0) {
+            for (int j = i; j <= n; j += i) {
+                a[j] = i;
+            }
+        }
+    }
+
+    for (int i = 1; i <= n; i++) {
+        if (a[i] <= b) {
+            cnt++;
+        }
+    }
+
+    cout << cnt << endl;
+
+    return 0;
+}