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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