Create 2563.py

Author: kapforty

python3/2563.py

@@ -0,0 +1,28 @@
+class Solution:
+    def countFairPairs(self, nums: List[int], lower: int, upper: int) -> int:
+        # trivial case
+        if len(nums) < 2:
+            return 0
+
+        def findM(target, l, r):
+            while l < r:
+                m = (l + r) // 2
+                if nums[m] < target:
+                    l = m + 1
+                else:
+                    r = m
+            return l
+                    
+        res = 0
+        nums.sort()
+        l, r = -1, len(nums) - 1
+        while l + 2 <= r:
+            l += 1
+            if nums[l] + nums[r] < lower:
+                continue
+            m = findM(lower - nums[l], l + 1, r)
+            while r >= m and nums[l] + nums[r] > upper:
+                r -= 1
+            if l < m and m <= r:
+                res += r - m + 1
+        return res