Count the Number of Fair Pairs
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 < nlower <= nums[i] + nums[j] <= upper
Example 1
Input
nums = [0,1,7,4,4,5], lower = 3, upper = 6Output
6There 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 = 11Output
1There is a single fair pair: (2,3).
Constraints
- 1 <= nums.length <= 10^5
- nums.length == n
- -10^9 <= nums[i] <= 10^9
- -10^9 <= lower <= upper <= 10^9