Move Zeroes

Move Zeroes
Problem Statement

Given an array, move all 0’s to the end while maintaining the relative order of non-zero elements.
The operation must be done in-place.

Example
Input: [0,1,0,3,12]
Output: [1,3,12,0,0]
Approach 1: Extra Array (Simple but Not In-place)
Idea

Store all non-zero elements

Add zeros at the end

Replace original array

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

temp = [i for i in nums if i != 0]
zeros = [0] * (len(nums) - len(temp))
nums[:] = temp + zeros

print(nums)
Complexity

Time: O(n)

Space: O(n)

But the problem requires in-place, so we need a better method.

Approach 2: Two Pointer Method (Best Solution)
Idea

Use a pointer j to place non-zero elements

Traverse array with i

If element is non-zero → swap with position j

Increment j

This keeps order and moves zeros automatically to end.

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

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

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

This is the optimal solution.