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

Medium

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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

Solution 1 : Less code than previous solution

class Solution:
    def searchRange(self, nums: List[int], target: int) -> List[int]:
        self.nums = nums
        self.target = target
        left = self.binary(True)
        if left == -1:
            return [-1,-1]
        right = self.binary()
        return [left, right]
        
    def binary(self, leftmost = False):
        target = self.target
        left = 0
        right = len(self.nums)
        index = -1
        while left < right:
            mid = left + (right-left) // 2
            if self.nums[mid] == target:
                index = mid
                if leftmost:
                    right = mid
                else:
                    left = mid + 1
            elif self.nums[mid] < target:
                left = mid + 1
            else:
                right = mid
        return index
        

class Solution:
    def searchRange(self, nums: List[int], target: int) -> List[int]:
        minIndex = self.findMinIndex(nums, target)
        maxIndex = self.findMaxIndex(nums, target)
        return [minIndex,maxIndex]
    
    def findMinIndex(self, nums, target, index=-1):
        low = 0
        high = len(nums)-1
        while low <= high:
            mid = low + (high-low)//2
            if nums[mid] == target:
                index = mid
                high = mid - 1
            elif nums[mid] > target:
                high = mid - 1
            else:
                low = mid + 1
        return index
    
    def findMaxIndex(self, nums, target, index=-1):
        low = 0
        high = len(nums)-1
        while low <= high:
            mid = low + (high-low)//2
            if nums[mid] == target:
                index = mid
                low = mid + 1
            elif nums[mid] > target:
                high = mid - 1
            else:
                low = mid + 1
        return index