Move Zeroes

Hi everyone!

Today I solved a simple but important array problem — moving all zeroes to the end while keeping the order of other elements same.

Problem

Given an array, move all 0s to the end while maintaining the order of non-zero elements.

Example:

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


Output: [1, 3, 12, 0, 0]

My Approach

At first, I thought of creating a new array, but the problem clearly says:

Do it in-place

So I used a pointer-based approach.

Logic

• Use a pointer insert to track position for non-zero elements


• Traverse the array:
  
  
  
  
  • If element is non-zero → place it at insert
    
  
  
  • Increment insert
    
  
  
  
  
  
  



• After that, fill remaining positions with 0
  

Code (Python)

from typing import List

class Solution:

def moveZeroes(self, nums: List[int]) -> None:

insert = 0

    for i in range(len(nums)):

        if nums[i] != 0:

            if i != insert:

                nums[insert] = nums[i]

            insert += 1



    for i in range(insert, len(nums)):

        nums[i] = 0

Time & Space Complexity

• Time: O(n)
  


• Space: O(1) (in-place)

Key Insight

We don’t need to swap every time — just overwrite non-zero elements and then fill zeros at the end.

What I Learned

• In-place problems need careful pointer handling


• Avoid unnecessary swaps to optimize performance


• Simple logic can still be very efficient

Thanks for reading!

Feel free to share any other approaches or improvements.