Simple example
Input
remove_consecutive_duplicates([1, 1, 2, 2, 1])
Output
[1, 2, 1]
Consecutive runs of 1 and 2 are collapsed, but the later 1 is kept because it's not consecutive with the earlier 1.
Full lesson preview
Remove Consecutive Duplicates
Return a new list with consecutive duplicate values collapsed to a single occurrence.
Python practice13 minLoops & IterationIntermediateLast updated March 15, 2026
Problem statement
Given a list, produce a new list where runs of the same value that appear consecutively are collapsed into a single occurrence. Non-consecutive duplicates (the same value separated by different values) should be preserved.
Implement remove_consecutive_duplicates(lst) that returns the cleaned list. The original list should not be modified.
Task
Learn to iterate through a sequence and build a result while comparing current and previous elements.
Examples
Input format
A single argument: lst (a list of values).
Output format
A list with consecutive duplicates removed.
Constraints
You may assume the input is a list. Elements can be of any type that supports equality comparison. Aim for linear time O(n) and O(n) additional space for the output.
Samples
Sample 1
Input
remove_consecutive_duplicates(['a', 'a', 'b', 'a'])
Output
['a', 'b', 'a']
Only consecutive 'a' at the start are collapsed; the later 'a' remains.