diff --git a/Leetcode-Hard/315-Count of Smaller Numbers After Self/Count of Smaller Numbers After Self.cpp b/Leetcode-Hard/315-Count of Smaller Numbers After Self/Count of Smaller Numbers After Self.cpp
new file mode 100644
index 0000000..6faec5e
--- /dev/null
+++ b/Leetcode-Hard/315-Count of Smaller Numbers After Self/Count of Smaller Numbers After Self.cpp	
@@ -0,0 +1,20 @@
+#include <ext/pb_ds/assoc_container.hpp>
+#include <ext/pb_ds/tree_policy.hpp>
+using namespace __gnu_pbds;
+#define ordered_set tree<int, null_type,less_equal<int>, rb_tree_tag,tree_order_statistics_node_update>
+
+
+class Solution {
+public:
+    vector<int> countSmaller(vector<int>& nums) {
+        ordered_set s;
+        vector<int>ans;
+        int n=(int)nums.size();
+        for(int i=n-1;i>=0;i--){
+            ans.push_back(s.order_of_key(nums[i]));
+            s.insert(nums[i]);
+        }
+        reverse(ans.begin(),ans.end());
+        return ans;
+    }
+};