🚚 Move Zeroes – Python (In-Place Solution)

Hi All,

Today I solved a popular problem: Move all zeroes to the end of the array while maintaining the order of non-zero elements.

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📌 Problem Statement

Given an array nums, move all 0s to the end while:

• Maintaining the relative order of non-zero elements
• Performing the operation in-place (no extra array)

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🔍 Examples

Example 1:

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

Output:

[1, 3, 12, 0, 0]

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Example 2:

nums = [0]

Output:

[0]

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💡 Approach

🔹 Two Pointer Technique (Optimal)

👉 Idea:

• Use a pointer j to track position for non-zero elements
• Traverse array with i
• Swap non-zero elements forward

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🧠 Step-by-Step Logic

1. Initialize j = 0
2. Traverse array:
   • If element is not zero:
     • Swap nums[i] with nums[j]
     • Increment j

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💻 Python Code

def moveZeroes(nums):
    j = 0

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

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🔍 Dry Run

For:

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

Steps:

• Swap 1 → [1, 0, 0, 3, 12]
• Swap 3 → [1, 3, 0, 0, 12]
• Swap 12 → [1, 3, 12, 0, 0]

Final Output:

[1, 3, 12, 0, 0]

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🖥️ Sample Output

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

Input: [0]
Output: [0]

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⚡ Complexity Analysis

• Time Complexity: O(n) ✅
• Space Complexity: O(1) ✅

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🧠 Why this is important?

• Uses two pointer technique
• Maintains order (stable)
• Common pattern in array problems

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✅ Conclusion

This problem helped me understand:

• In-place array manipulation
• Efficient element shifting
• Two pointer strategy

🚀 A must-know problem for beginners and interviews!

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