Find First and Last Position in Sorted Array

Problem
Given a sorted array of integers and a target value, find the index of the first and the last occurrence of the target. If the target is not present, return [-1, -1]. Aim for O(log n) time.

Input / Output

• Input: a non-decreasing integer array nums and an integer target.
• Output: [firstIndex, lastIndex], or [-1, -1] if the target is absent.

Constraints

• 0 <= nums.length <= 10^5
• Array is sorted non-decreasing; duplicates may exist.
• Required time complexity: O(log n).

Example

• nums = [5,7,7,8,8,10], target = 8 -> [3,4]
• nums = [5,7,7,8,8,10], target = 6 -> [-1,-1]