From 360c74a2ba246228936ed04875f1fe266815e3d7 Mon Sep 17 00:00:00 2001
From: chayan das <dasshuvo817@gmail.com>
Date: Sat, 19 Apr 2025 19:47:23 +0530
Subject: [PATCH] Create 2563. Count the Number of Fair Pairs1

---
 2563. Count the Number of Fair Pairs1 | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)
 create mode 100644 2563. Count the Number of Fair Pairs1

diff --git a/2563. Count the Number of Fair Pairs1 b/2563. Count the Number of Fair Pairs1
new file mode 100644
index 0000000..9a2aae5
--- /dev/null
+++ b/2563. Count the Number of Fair Pairs1	
@@ -0,0 +1,23 @@
+class Solution {
+public:
+    long long countFairPairs(vector<int>& nums, int lower, int upper) {
+        sort(nums.begin(), nums.end());
+        return lower_bound(nums, upper + 1) - lower_bound(nums, lower);
+    }
+
+private:
+    long long lower_bound(vector<int>& nums, int value) {
+        int left = 0, right = nums.size() - 1;
+        long long result = 0;
+        while (left < right) {
+            int sum = nums[left] + nums[right];
+            if (sum < value) {
+                result += (right - left);
+                left++;
+            } else {
+                right--;
+            }
+        }
+        return result;
+    }
+};