34. Find First and Last Position of Element in Sorted Array

Given an array of integers nums sorted in non-decreasing order, find the starting and ending position of a given target value

Example 1:

• Input: nums = [5,7,7,8,8,10], target = 8
• Output: [3,4]

Example 2:

• Input: nums = [5,7,7,8,8,10], target = 6
• Output: [-1,-1]

Example 3:

• Input: nums = [], target = 0
• Output: [-1,-1]

Constraints:

• 0 <= nums.length <= 10^5
• -10^9 <= nums[i] <= 10^9
• nums is a non-decreasing array.
• -10^9 <= target <= 10^9

Solution

class Solution:
    def searchRange(self, nums: list[int], target: int) -> list[int]:
        def find(first):
            result = -1
            left, right = 0, len(nums) - 1
            while left <= right:
                mid = (left + right) // 2
                if nums[mid] == target:
                    result = mid
                    if first:
                        right = mid - 1
                    else:
                        left = mid + 1
                elif nums[mid] < target:
                    left = mid + 1
                else:
                    right = mid - 1
            return result

        return [find(True), find(False)]