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Reverse even numbers in a list | Upstart Coding Question

Quick Overview

This question evaluates competency in basic array manipulation, specifically filtering elements by parity and reversing their order while preserving no other ordering constraints.

Reverse even numbers in a list

Company: Upstart

Role: Software Engineer

Category: Coding & Algorithms

Difficulty: medium

Interview Round: Technical Screen

Given an integer array `nums`, remove all odd numbers and return the remaining even numbers in reverse order (preserving no other ordering constraints). Example: - Input: `nums = [2, 3, 4]` - Output: `[4, 2]` Clarifications: - `0` is even. - If no even numbers exist, return an empty array.

Quick Answer: This question evaluates competency in basic array manipulation, specifically filtering elements by parity and reversing their order while preserving no other ordering constraints.

Given an integer array `nums`, remove all odd numbers and return the remaining even numbers in **reverse order** of their appearance in the original array. In other words, scan the array from right to left and collect every even value you encounter. **Example:** - Input: `nums = [2, 3, 4]` - Output: `[4, 2]` **Clarifications:** - `0` is even. - Negative even numbers (e.g. `-2`) count as even. - If no even numbers exist, return an empty array. - Duplicate even values are all kept.

Constraints

0 <= nums.length <= 10^5
-10^9 <= nums[i] <= 10^9

Examples

Input: ([2, 3, 4],)

Expected Output: [4, 2]

Explanation: Scanning right-to-left: 4 (even, keep), 3 (odd, skip), 2 (even, keep) -> [4, 2].

Input: ([],)

Expected Output: []

Explanation: Empty input yields an empty result.

Input: ([1, 3, 5, 7],)

Expected Output: []

Explanation: No even numbers, so the result is empty.

Input: ([0, 2, 4, 6],)

Expected Output: [6, 4, 2, 0]

Explanation: All even; reversed order is 6, 4, 2, 0. Note 0 is even.

Input: ([2, 2, 3, 2],)

Expected Output: [2, 2, 2]

Explanation: Duplicate evens are all kept; the odd 3 is removed.

Input: ([-4, -3, -2, 1],)

Expected Output: [-2, -4]

Explanation: Negative evens count: right-to-left gives -2, then -4.

Input: ([5],)

Expected Output: []

Explanation: Single odd element produces an empty result.

Input: ([8],)

Expected Output: [8]

Explanation: Single even element is returned as-is.

Hints

Iterate over the array from the last element to the first.
Keep only the values that are divisible by 2 (use the modulo operator: x % 2 == 0). Remember that 0 and negative numbers can be even too.
Equivalently, filter the evens first then reverse the result — both give the same order.

Last updated: Jun 26, 2026

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