Binary Search (and Variants)

Problem

Implement binary search, then extend it to find the first and last occurrence of a target in a sorted array that may contain duplicates.

Input / Output

• Input: a sorted array nums and a target value.
• Output: the target's index (plain search), or the first and last indices of the target (variant), or -1 if absent.

Constraints

• 1 ≤ n ≤ 10^5
• The array is sorted and may contain duplicates.

Example

[1,2,2,2,3], target=2 -> first=1, last=3