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

Medium

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

# @param {Integer[]} nums
# @param {Integer} target
# @return {Integer[]}
def search_range(nums, target)
  ans = [helper(nums, target, false), helper(nums, target, true)]
  ans
end

private

def helper(nums, target, equals)
  l = 0
  r = nums.length - 1
  result = -1

  while l <= r
    mid = l + (r - l) / 2
    result = mid if nums[mid] == target
    if nums[mid] < target || (nums[mid] == target && equals)
      l = mid + 1
    else
      r = mid - 1
    end
  end

  result
end

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