added new file in c++ repo

C++/Reverse_pair.cpp

@@ -0,0 +1,58 @@
+class Solution {
+public: 
+    int pairCount = 0;
+
+    void merge(vector<int>& nums, int low, int mid, int high) {
+        int total = 0;
+        int i = low;
+        int j = mid + 1;
+         // Counting the number of pairs satisfying the condition nums[i] > 2 * nums[j]
+        while (i <= mid) {
+            while (j <= high && nums[i] > (long long)2 * nums[j]) {
+                j++;
+            }
+            total += (j - (mid + 1));
+            i++;
+        }
+
+        vector<int> temp;
+        i = low;
+        j = mid + 1;
+
+        while (i <= mid && j <= high) {
+            if (nums[i] < nums[j]) {
+                temp.push_back(nums[i++]);
+            } else {
+                temp.push_back(nums[j++]);
+            }
+        }
+
+        while (i <= mid) {
+            temp.push_back(nums[i++]);
+        }
+
+        while (j <= high) {
+            temp.push_back(nums[j++]);
+        }
+
+        for (int it = low; it <= high; it++) {
+            nums[it] = temp[it - low];
+        }
+
+        pairCount += total;
+    }
+
+    void mergeSort(vector<int>& nums, int low, int high) {
+        if (low < high) {
+            int mid = low + (high - low) / 2;
+            mergeSort(nums, low, mid);
+            mergeSort(nums, mid + 1, high);
+            merge(nums, low, mid, high);
+        }
+    }
+
+    int reversePairs(vector<int>& nums) {
+        mergeSort(nums, 0, nums.size() - 1);
+        return pairCount;
+    }
+};

README.md

@@ -103,6 +103,8 @@ Check out ---> [Sample PR](https://github.com/codedecks-in/LeetCode-Solutions/pu
 | #   | Title                                                                                   | Solution                                    | Time   | Space  | Difficulty | Tag | Tutorial |
 | --- | --------------------------------------------------------------------------------------- | ------------------------------------------- | ------ | ------ | ---------- | --- | -------- |
 | 973 | [K Closest Points to Origin](https://leetcode.com/problems/k-closest-points-to-origin/) | [C++](./C++/k-closest-points-to-origin.cpp) | _O(n)_ | _O(1)_ | Medium     |     |          |
+| 493 | [Reverse Pairs](https://leetcode.com/problems/reverse-pairs) | [C++](./C++/reverse_pair.cpp)
+| _O(n log n)_ | _O(n)_ | Hard    |     |          |
 
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