My Thinking and Approach

Introduction

In this problem, I was given an integer array and asked to move all the 0s to the end while maintaining the relative order of the non-zero elements.

At first glance, it looked simple. But the constraint that the operation must be done in-place (without using extra space) made me think more carefully about the solution.

Problem Statement

• Move all 0s to the end of the array


• Maintain the order of non-zero elements


• Do it in-place (no extra array allowed)

My Initial Approach

Initially, I thought of a straightforward method:

• Create a new array


• Add all non-zero elements


• Then append all zeros at the end

But this approach uses extra space, which violates the problem constraint.

So I needed a more optimized solution.

Optimized Approach (Two Pointer Technique)

To solve this efficiently, I used the two-pointer approach.

Idea

• Use one pointer i to traverse the array


• Use another pointer j to track the position where the next non-zero element should be placed

Steps

1. Initialize j = 0
   


2. Traverse the array using i
   


3. If nums[i] != 0:

• Swap nums[i] with nums[j]
  


• Increment j
  
  
  
  
  1. Continue till the end of the array
  
  
  
  

Code (Java)

class Solution {

    public void moveZeroes(int[] nums) {

        int j = 0;



        for (int i = 0; i < nums.length; i++) {

            if (nums[i] != 0) {

                int temp = nums[i];

                nums[i] = nums[j];

                nums[j] = temp;

                j++;

            }

        }

    }

}

Example

Input:

[0, 1, 0, 3, 12]

Step-by-step execution:

• i = 0 → value = 0 → skip


• i = 1 → value = 1 → swap with index