From 984169e6c7317e2e7bc8a666b457375042e25cd7 Mon Sep 17 00:00:00 2001
From: STUTI MISHRA <153292796+stutimi@users.noreply.github.com>
Date: Thu, 30 Oct 2025 20:27:00 +0530
Subject: [PATCH] Create 493_Reverse_Pairs

---
 493_Reverse_Pairs | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)
 create mode 100644 493_Reverse_Pairs

diff --git a/493_Reverse_Pairs b/493_Reverse_Pairs
new file mode 100644
index 0000000..c62dcee
--- /dev/null
+++ b/493_Reverse_Pairs
@@ -0,0 +1,26 @@
+class Solution {
+public:
+    int reversePairs(vector<int>& a) { return (int)ms(a, 0, (int)a.size() - 1); }
+
+private:
+    long long ms(vector<int>& a, int l, int r) {
+        if (l >= r) return 0;
+        int m = (l + r) >> 1;
+        long long cnt = ms(a, l, m) + ms(a, m + 1, r);
+
+        int j = m + 1;
+        for (int i = l; i <= m; ++i) {
+            while (j <= r && (long long)a[i] > 2LL * a[j]) ++j;
+            cnt += j - (m + 1);
+        }
+
+        vector<int> t; t.reserve(r - l + 1);
+        int i = l; j = m + 1;
+        while (i <= m && j <= r) t.push_back(a[i] <= a[j] ? a[i++] : a[j++]);
+        while (i <= m) t.push_back(a[i++]);
+        while (j <= r) t.push_back(a[j++]);
+        for (int k = l; k <= r; ++k) a[k] = t[k - l];
+
+        return cnt;
+    }
+};