283. Move Zeroes

Quick Identifier

Topic: two-pointers
Pattern: stable overwrite pointer
Difficulty: Easy
Companies: Amazon, Facebook, Bloomberg, Apple, Adobe
Frequency: High
LeetCode: 283
Hint: write is the next position for a non-zero. read scans every value once.

Quick Sights

Time Complexity: O(n) - one read pass plus zero fill.
Space Complexity: O(1) - in-place mutation.
Core Mechanism: Copy non-zero values forward with write, then fill the remaining suffix with zeroes.

Concept Explanation

This is a stable partition. Non-zero values must keep their relative order, and zeroes move behind them.

The invariant is: everything before write is the final non-zero prefix. The read pointer scans the original data. Every non-zero is promoted to write; zeroes are ignored until the suffix fill.

Diagram

This diagram shows the pointer decisions and the step-by-step algorithm flow.

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Study Pattern (SDE3+)

0-3 min: Name the pointer shape, then state the invariant and discard rule before coding.
Implementation pass: Keep pointer movement explicit; every branch must return, record an answer, or move at least one pointer.
5 min extension: Explain how the solution changes for immutable input, streaming input, many duplicate values, or many repeated queries.

Approaches

Extra array is easy but O(n) space. Swapping works too. Stable overwrite plus zero fill is easy to explain and constant space.

Optimal Solution

JavaScript

function moveZeroes(nums) {
	let write = 0;
	for (let read = 0; read < nums.length; read++) {
		if (nums[read] !== 0) nums[write++] = nums[read];
	}
	while (write < nums.length) nums[write++] = 0;
}

Go

func moveZeroes(nums []int) {
	write := 0
	for read := 0; read < len(nums); read++ {
		if nums[read] != 0 {
			nums[write] = nums[read]
			write++
		}
	}
	for write < len(nums) {
		nums[write] = 0
		write++
	}
}