Move Zeroes: Understanding Parameter Behavior in Python

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🖋️ Move Zeroes

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

Note that you must do this in-place without making a copy of the array.

Example 1:

Here's an example of solving the "Move Zeroes" problem (a wrong one):

In this code, the final assignment to nums actually doesn’t affect the parameter nums because they are different variables.

Within the function, Python creates a new namespace, known as the local scope. All variables defined or assigned inside the function are, by default, considered local variables.

When you execute nums = nums + [0] * counter inside the function, Python’s interpreter assigns the new list object (from the right-hand expression) to the local variable nums. This means:

The original nums (the parameter) still refers to the passed-in list object.

The local variable nums now refers to a new list object.

The assignment nums = ... changes the binding of the local nums to point to the new object, leaving the original passed-in list unaffected.

A possible solution is to change the first nums to nums[:], which means you are modifying the original object.

Two-pointer Solution:

A more efficient approach to solving the "Move Zeroes" problem is using a two-pointer method:

In this solution, left is initialized to zero, and the first element being zero does not affect the algorithm's ability to move all zeros to the right. This two-pointer method efficiently processes the list in-place, making it a more optimal solution than the previous approach.