ASSIGNMENT 13

Move All Zeros to the End (In-Place & Stable)

Rearranging arrays efficiently is a key skill in coding interviews.
Let’s solve a classic problem: moving all zeros to the end while maintaining order

Problem Statement

Given an integer array nums, move all 0s to the end of the array.

Constraints:
Maintain the relative order of non-zero elements
Perform the operation in-place
Do not create a copy of the array .

Examples:
Example 1
Input: [0, 1, 0, 3, 12]
Output: [1, 3, 12, 0, 0]
Example 2
Input: [0]
Output: [0]
Optimal Approach: Two-Pointer Technique

We use a two-pointer approach to solve this efficiently.

i → scans the array
j → tracks position to place next non-zero element

-Move all non-zero elements forward
-Fill remaining positions with 0s

This ensures:

Order is preserved .
No extra space is used .

~ Algorithm Steps ;

Initialize j = 0
Traverse array using i
If nums[i] != 0:
Swap nums[i] with nums[j]
Increment j
Continue till end

Python Implementation
def move_zeros(nums):
j = 0 # position for next non-zero

for i in range(len(nums)):

    if nums[i] != 0:

        nums[i], nums[j] = nums[j], nums[i]

        j += 1

Example usage

nums = [0, 1, 0, 3, 12]
move_zeros(nums)
print(nums)

~ Key Takeaways :
Uses two-pointer technique
Maintains relative order (stable)
Works in-place
Very common interview problem