Move Zeroes - CA13

My Thinking and Approach

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Introduction

In this problem, I was given an array of integers and asked to move all zeroes to the end of the array.

The important condition is that the relative order of non-zero elements should be maintained.

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Problem Statement

• Given an array of integers nums

• Move all 0’s to the end

• Conditions:

  • Maintain relative order of non-zero elements
  • Perform operation in-place
  • Do not use extra space

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My Initial Thought

At first, I considered:

• Creating a new array
• Adding all non-zero elements
• Then adding zeroes at the end

But this approach uses extra space.

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Key Observation

Instead of using extra space:

• I can shift all non-zero elements to the front
• Then fill the remaining positions with zeroes

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Optimized Approach

I decided to use a pointer to track position of non-zero elements.

Logic:

• Traverse the array
• Place non-zero elements at correct position
• Fill remaining positions with zeroes

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My Approach (Step-by-Step)

1. Initialize a pointer pos = 0
2. Traverse the array:

• If element is not zero
  → place it at index pos
  → increment pos

  1. After traversal:

• Fill remaining elements with 0

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Code (Python)

Below is the implementation clearly separated inside a code block:

class Solution:
    def moveZeroes(self, nums):
        pos = 0

        for i in range(len(nums)):
            if nums[i] != 0:
                nums[pos] = nums[i]
                pos += 1

        for i in range(pos, len(nums)):
            nums[i] = 0

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Example Walkthrough

Input:

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

Steps:

• Move non-zero elements → [1, 3, 12, _, _]
• Fill remaining with zeroes → [1, 3, 12, 0, 0]

Output:

[1, 3, 12, 0, 0]

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Complexity Analysis

Type	Complexity
Time Complexity	O(n)
Space Complexity	O(1)

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Key Takeaways

• In-place modification is important
• Two-pass solution is efficient
• Maintaining order is key

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Conclusion

This problem helped me understand how to rearrange elements efficiently while maintaining order and without using extra space.

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