Optimize partitioning for O(n) time

Last updated: September 21, 2025

Quick Overview

Given an array of integers, partition the array into two subsets such that all elements in one subset are less than or equal to a specified pivot value, and all elements in the other subset are greater than the pivot. The solution should achieve this partitioning in O(n) time complexity, returning the rearranged array as the output.

Walmart
Coding & Algorithms
Software Engineer
Walmart
September 21, 2025
Software Engineer
Take-home Project
Coding & Algorithms
Easy

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Given an array of integers, partition the array into two subsets such that all elements in one subset are less than or equal to a specified pivot value, and all elements in the other subset are greater than the pivot. The solution should achieve this partitioning in O(n) time complexity, returning the rearranged array as the output.

How to Approach This
  1. Clarify input constraints and edge cases before writing code.
  2. Walk through your approach verbally and confirm with the interviewer before coding.
  3. Start with a brute force solution, then optimize. Mention time and space complexity.
  4. Test your solution with examples, including edge cases like empty input or duplicates.
  5. Consider common patterns: sliding window, two pointers, hash map, BFS/DFS, dynamic programming.
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Problem Analysis

The problem requires partitioning an array into two subsets based on a pivot value. This suggests the use of the two pointers approach, where one pointer starts from the beginning of the array (le...

Approach
  1. Initialize two pointers: left at the start (index 0) and right at the end (index len(array) - 1) of the array.
  2. While left is less than or equal to right:
    • If the element at `array[le...

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