Given a sorted list nums (duplicates allowed) and two integers lo <= hi, return how many elements x
satisfy lo <= x <= hi.
Examples
Input: nums = [1, 2, 2, 3, 5, 8], lo = 2, hi = 5
Output: 4
Explanation: 2, 2, 3 and 5 are inside the range.
Input: nums = [1, 2, 2, 3, 5, 8], lo = 4, hi = 4
Output: 0
Constraints
0 <= len(nums) <= 10**6-10**9 <= nums[i], lo <= hi <= 10**9- Required time:
O(log n)per call. Counting one by one is too slow.
Goals
- Distinguish the first index >= x from the first index > x
- Combine two boundary searches into a count