Solution as on 06-03-2022 07:45 am

Author: knockcat

1359. Count All Valid Pickup and Delivery Options.cpp

@@ -0,0 +1,28 @@
+// 1359.✅ Count All Valid Pickup and Delivery Options
+
+class Solution
+{
+public:
+    int countOrders(int n)
+    {
+        long res = 1, mod = 1000000007;
+        for (int i = 1; i <= n; ++i)
+        {
+            // calulating n!
+            res *= i;
+            // to avoid overflow
+            res %= mod;
+
+            // (2*i-1) are the vacant places which we can choose
+            // later we have n! permutation of pickup task
+            // therefore we have to multiply with n! that we calculated as res.
+            res *= (2 * i - 1);
+
+            // to avoid overflow
+            res %= mod;
+        }
+
+        // to avoid overflow
+        return res % mod;
+    }
+};