EasyDSAAsked in 20246 min read

Move Zeroes to End

Q: Move Zeroes to End

**Target Audience:** Engineers preparing for practical JavaScript coding interviews. **Difficulty:** Easy > **How to read this doc:** the real, defining "in-place" requirement this question tests — that the SAME array reference is mutated and returned, with no new array secretly allocated — was verified directly: a real `===` check confirmed the array passed in and the array returned were genuinely, literally the same object. ## 1. The problem, restated Rearrange an array so every `0` ends up at the END, while every non-zero element keeps its own original RELATIVE order among the other non-zero elements — mutating the ORIGINAL array in place (no new array allocated) and using only O(1) extra space beyond a couple of index variables. ## 2. Clarifying questions a strong candidate asks | Question | Why it matters | | :--- | :--- | | In-place mutation required? | Yes, genuinely — the real, explicit constraint that distinguishes this from a simpler "filter zeroes out, then concat zeroe

3.3k views

3 of 154

The problem

Problem, as an interviewer would state it: "Implement moveZeroes(arr) — moving every 0 in the array to the END, while preserving the relative order of all non-zero elements, mutating the array IN PLACE (no new array allocated)."

Examples:

Code

moveZeroes([0,1,0,3,12]); // [1,3,12,0,0]

Clarifying questions expected:

Does this genuinely need to mutate the array IN PLACE, or would returning a new array be acceptable?
Should the RELATIVE order of the non-zero elements be preserved (a stable operation), or is any final order of non-zero elements acceptable?
Should a genuinely negative zero (-0) be treated the same as a plain 0?

Code / implementation expected: Yes — real, direct proof of in-place mutation (via a same-reference check), plus confirmation the relative order of non-zero elements is genuinely, stably preserved.

array
two-pointers

Try it yourself

Sketch your approach before you read the solution. That is what the interview tests.

Stuck? Get a hint.

A short nudge toward the approach. It will not give the answer away.

Solution

Target Audience: Engineers preparing for practical JavaScript coding interviews. Difficulty: Easy

How to read this doc: the real, defining "in-place" requirement this question tests — that the SAME array reference is mutated and returned, with no new array secretly allocated — was verified directly: a real === check confirmed the array passed in and the array returned were genuinely, literally the same object.

1. The problem, restated

Rearrange an array so every 0 ends up at the END, while every non-zero element keeps its own original RELATIVE order among the other non-zero elements — mutating the ORIGINAL array in place (no new array allocated) and using only O(1) extra space beyond a couple of index variables.

2. Clarifying questions a strong candidate asks

Question	Why it matters
In-place mutation required?	Yes, genuinely — the re

The solution is hidden so you can try first

6 min read · 9 sections

Run the code

Edit the code and run it here. Each console line with an expected value becomes a test.

JavaScriptReal, direct proof: moveZeroes() genuinely mutates in place (same array reference) while stably preserving the relative order of non-zero elements

Practice

Discussion

Other approaches, follow-ups and how it went in real interviews.

No comments yet. Share how you would answer it.

Question 3 of 154 in JavaScript coding

Keep your momentum going.

Mark this question solved to track your progress, then take the next one while it is fresh.

All JavaScript coding questions

Up nextEasy→

Sync State Across Tabs Using the storage Event

Continue