Onsite Interview (Phenom)
- Posted
- 27 Feb 2026
Summary
During my onsite interview with Phenom, I was presented with a coding challenge to sort an array containing only 0s, 1s, and 2s in-place, aiming for O(n) time and O(1) space complexity.
How it went
You are given an integer array nums containing only 0, 1, and 2.
Sort the array in-place so that:
-
All 0s appear first
-
Followed by all 1s
-
Followed by all 2s
You must:
-
Solve it in O(n) time complexity
-
Use O(1) extra space (in-place sorting)
-
Avoid using built-in sort functions
Example
- Input
- nums = [2,0,0,0,1,1,1,2,2,1,0,2]
- Output
- [0,0,0,0,1,1,1,2,2,2,2,2]
Constraints
1 <= nums.length <= 10^5
nums[i] is either 0, 1, or 2
Follow-up Can you solve this problem in a single pass?
Questions asked (1)
- 01
Sort Array of 0s, 1s, and 2s (Dutch National Flag Problem)
Data Structures & Algorithms · Medium
You are given an integer array nums containing only 0, 1, and 2.
Sort the array in-place so that:
-
All 0s appear first
-
Followed by all 1s
-
Followed by all 2s
You must:
-
Solve it in O(n) time complexity
-
Use O(1) extra space (in-place sorting)
-
Avoid using built-in sort functions
Example
- Input
- nums = [2,0,0,0,1,1,1,2,2,1,0,2]
- Output
- [0,0,0,0,1,1,1,2,2,2,2,2]
Constraints
1 <= nums.length <= 10^5 nums[i] is either 0, 1, or 2Follow-up Can you solve this problem in a single pass?
-