Count the Number of Fair Pairs

arraytwo pointersbinary search

Given a 0-indexed integer array nums of size n and two integers lower and upper , return the number of fair pairs .

A pair (i, j) is fair if:

0 <= i < j < n , and

lower <= nums[i] + nums[j] <= upper

Example 1

Input: nums = [0,1,7,4,4,5], lower = 3, upper = 6
Output: 6
There are 6 fair pairs: (0,3), (0,4), (0,5), (1,3), (1,4), and (1,5).

Example 2

Input: nums = [1,7,9,2,5], lower = 11, upper = 11
Output: 1
There is a single fair pair: (2,3).

1 <= nums.length <= 10 ^5

nums.length == n

-10 ^9 <= nums[i] <= 10 ^9

-10 ^9 <= lower <= upper <= 10 ^9

🤔

Medium

Difficulty

Topic Info

ModuleDSA

CategoryArray

Sub-topicTwo Pointers