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

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

Posted at 17:12h in Coding by
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Given an array of integers nums sorted in non-decreasing order, find the starting and ending position of a given target value.

If target is not found in the array, return [-1, -1].

You must write an algorithm with O(log n) runtime complexity.

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 <= 105
  • -109 <= nums[i] <= 109
  • nums is a non-decreasing array.
  • -109 <= target <= 109

 

class Solution:
    def searchRange(self, nums: List[int], target: int) -> List[int]:
        def binarySearchLeft(nums, target):
            left = 0
            right = len(nums) – 1
            while left <= right:
                middle = left + (right – left)//2
                if nums[middle] < target:
                    left = middle + 1
                else:
                    right = middle – 1
            return left
       
        def binarySearchRight(nums, target):
            left = 0
            right = len(nums) – 1
            while left <= right:
                middle = left + (right – left)//2
                if nums[middle] <= target:
                    left = middle + 1
                else:
                    right = middle – 1
            return right
       
        left = binarySearchLeft(nums, target)
        right = binarySearchRight(nums, target)
        print(left)
        print(right)
        if left <= right:
            return [left, right]
        else:
            return [-1, -1]
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