Move Zeroes in an Array

Introduction

Rearranging elements in an array while maintaining order is a common problem in programming. One such important problem is moving all zeroes to the end of the array without disturbing the order of non-zero elements.

This problem helps in understanding in-place operations and efficient array manipulation.

Problem Statement

Given an integer array nums, move all 0s to the end while maintaining the relative order of non-zero element

Example

Input:

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

Output:

[1, 3, 12, 0, 0]

Approach: Two-Pointer Method

We use:

• j position to place the next non-zero element

Steps:

1. Traverse the array
2. If element is non-zero:

• Swap it with position j
• Increment j

Python Implementation

def move_zeroes(nums):
    j = 0 

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

    return nums

# Example usage
nums = [0, 1, 0, 3, 12]
print(move_zeroes(nums))

Step-by-Step Example

For:

[0, 1, 0, 3, 12]

• i = 0 then skip (0)
• i = 1 then swap = [1, 0, 0, 3, 12]
• i = 3 then swap = [1, 3, 0, 0, 12]
• i = 4 then swap = [1, 3, 12, 0, 0]

Final result: [1, 3, 12, 0, 0]

Key Points

• Maintains order of non-zero elements
• Works in-place
• Efficient single traversal
• Common interview problem

Conclusion

The Move Zeroes problem is a great example of using the two-pointer technique to efficiently rearrange elements in an array. It avoids unnecessary operations and ensures optimal performance.

Understanding this pattern will help in solving many similar array manipulation problems.