283. Move Zeroes

At a Glance

• Topic: two-pointers
• Pattern: Two Pointers
• Difficulty: Easy
• Companies: Amazon, Facebook, Bloomberg, Apple, Adobe
• Frequency: High
• LeetCode: 283

Problem (one-liner)

Given an integer array nums, move all 0s to the end while preserving the relative order of non-zero elements. Must be in-place.

Recognition Cues

• "Move zeros to end"
• "Preserve relative order of non-zeros"
• In-place array transformation

Diagram

At-a-glance flow (replace with problem-specific Mermaid as you refine this note). camelCase node IDs; no spaces in IDs.

Approaches

• Brute force — build new array — O(n) time / O(n) space — disallowed if in-place only.
• Better — count non-zeros then second fill — two passes O(n) / O(1).
• Optimal — single pass write pointer — O(n) time / O(1) space — swap or assign non-zeros forward.

Optimal Solution

Go

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

JavaScript

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

Walkthrough

Input: nums = [0,1,0,3,12]

Invariant: [0..write-1] has all non-zeros in original encounter order; zeros drift right via swaps.

Edge Cases

• No zeros
• All zeros
• Single element

Pitfalls

• Second loop filling zeros from write onward when using assign-only variant (here swap handles zeros implicitly)

Similar Problems

• 75. Sort Colors — multi-value partitioning.
• 27. Remove Element — same write-pointer pattern (if file exists; else use index naming).
• 125. Valid Palindrome — two indices discipline.

Variants

• Move zeros while counting swaps (minimum swap variant).
• Stable partition without swapping (copy twice) if extra buffer allowed.

Mind-Map Tags

#two-pointers #in-place #partition #stable-order #swap-write