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Find First and Last Position of Element in Sorted Array Test | Pre-employment assessment - Testlify
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Find First and Last Position of Element in Sorted Array Test

Overview of Find First and Last Position of Element in Sorted Array Test

The goal of the problem is to find the first and last position or index value of the given target value.

Skills measured

  • binary search
  • Two pointers

Available in

English

Type

Coding Test


Time

30 Mins


Level

Intermediate


Questions

0

Use of Find First and Last Position of Element in Sorted Array test

The solution approach of the problem is to initialize two pointers, left and right, which represent the boundaries of the search range. Initially, set left = 0 and right = len(nums) - 1.
a. Calculate the mid index as mid = (left + right) // 2.
b. If the value at nums[mid] is greater than or equal to the target, update right = mid - 1 to search the left half of the array.
c. If the value at nums[mid] is less than the target, update left = mid + 1 to search the right half of the array.
Repeat steps b-c until left > right.
After the binary search, check if the value at index left is equal to the target. If it is not, return [-1, -1] since the target is not present in the array.
If the value at index left is equal to the target, it represents the leftmost occurrence of the target in the array.
We can then perform a second binary search to find the rightmost occurrence of the target. Let's call this function findRightPosition(nums, target).
Re-initialize left and right to the original values: left = 0 and right = len(nums) - 1.
a. Calculate the mid index as mid = (left + right) // 2.
b. If the value at nums[mid] is greater than the target, update right = mid - 1 to search the left half of the array.
c. If the value at nums[mid] is less than or equal to the target, update left = mid + 1 to search the right half of the array.
Repeat steps b-c until left > right.
After the binary search, check if the value at index right is equal to the target. If it is not, decrement right by 1 to obtain the index of the rightmost occurrence of the target.
Finally, return the results as [left, right], representing the first and last positions of the target in the sorted array.

Relevant for

  • Software Developer Engineer
  • Software Developer
  • Software Engineer

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1

binary search

Binary search is a fundamental algorithmic skill that involves searching for a specific target value within a sorted array by repeatedly dividing the search interval in half. In the context of finding the first and last position of an element in a sorted array, binary search helps efficiently locate the starting and ending indices of the target value. This skill is crucial for optimizing search algorithms and improving the performance of algorithms that involve searching for specific elements in sorted data structures. Mastering binary search can lead to faster and more efficient solutions for a wide range of problems in computer science and programming.

2

Two pointers

The two pointers skill covered in Find First and Last Position of Element in Sorted Array involves using two pointers to efficiently search for the first and last occurrence of a target element in a sorted array. By maintaining two pointers that move in opposite directions towards the target element, we can quickly identify the desired positions without unnecessary iterations. This approach is important as it significantly reduces the time complexity of the search operation, making it more efficient and practical for large datasets. Additionally, it helps in optimizing the overall performance of the algorithm by minimizing unnecessary comparisons and iterations.

The Find First and Last Position of Element in Sorted Array test is created by a subject-matter expert

Testlify’s skill tests are designed by experienced SMEs (subject matter experts). We evaluate these experts based on specific metrics such as expertise, capability, and their market reputation. Prior to being published, each skill test is peer-reviewed by other experts and then calibrated based on insights derived from a significant number of test-takers who are well-versed in that skill area. Our inherent feedback systems and built-in algorithms enable our SMEs to refine our tests continually.

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