Given an integer array nums, return the number of range sums that lie in [lower,
upper] inclusive.
Range sum S(i, j) is defined as the sum of the elements in nums
between indices i and j (i ≤ j),
inclusive.
Note:
A naive algorithm of O(n2) is trivial. You MUST do better than
that.
Example:
Input: nums =[-2,5,-1], lower =-2, upper =2, Output: 3 Explanation: The three ranges are :[0,0],[2,2],[0,2]and their respective sums are:-2, -1, 2.