Find kth largest element in array
Last updated: October 27, 2025
Quick Overview
Given an unsorted array of integers, write a function to find the kth largest element in the array. The function should take the array and an integer k as input and return the kth largest element. You may assume that k is always valid, and the array has at least k elements.
Doordash
October 27, 202514
15
3,423 solved
Given an unsorted array of integers, write a function to find the kth largest element in the array. The function should take the array and an integer k as input and return the kth largest element. You may assume that k is always valid, and the array has at least k elements.
This coding problem is frequently asked during Onsite at Doordash. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Doordash expects candidates to write production-quality code, not just solve the puzzle.
What the Interviewer Expects
- Recognize the underlying problem pattern (sliding window, two pointers, BFS/DFS, etc.)
- Discuss multiple approaches and trade-offs before coding
- Implement an optimal solution with clean, production-quality code
- Handle all edge cases including boundary conditions and invalid input
- Optimize both time and space complexity with clear justification
- Test your solution systematically with well-chosen examples
Key Topics to Cover
How to Approach This
- Clarify input constraints and edge cases before writing code.
- Walk through your approach verbally and confirm with the interviewer before coding.
- Start with a brute force solution, then optimize. Mention time and space complexity.
- Test your solution with examples, including edge cases like empty input or duplicates.
- Consider common patterns: sliding window, two pointers, hash map, BFS/DFS, dynamic programming.
Possible Follow-up Questions
- Can you optimize the space complexity of your solution?
- How would you parallelize this solution?
- Can you solve this in a single pass?
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Problem Analysis
The problem of finding the kth largest element in an unsorted array can be efficiently solved using the Quickselect algorithm, which is a variation of the QuickSort. This approach is suitable because ...
Approach
- Choose a Pivot: We can choose a pivot randomly from the array.
- Partition the Array: Rearrange the elements such that all elements greater than the pivot are on one side, and all elements...
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