Problem 10: Duplicate Removal

Source: Dev.to

Problem Description

We need a function that removes duplicates from a list while preserving the original order of elements.

Example
remove_duplicates([1, 2, 2, 3, 1, 4]) should return [1, 2, 3, 4].

Solution

def remove_duplicates(lst):
    """
    Removes duplicates from a list while maintaining order.
    """
    seen = set()
    result = []

    for i in lst:
        if i not in seen:
            seen.add(i)
            result.append(i)
    return result

# Test case
print(remove_duplicates([1, 2, 2, 3, 1, 4]))
# Output: [1, 2, 3, 4]

Explanation

1. Initialize

   • seen = set() – stores elements that have already been encountered.
   • result = [] – will contain the final list without duplicates.

2. Iterate through the input list

   for i in lst:

   • If i is not in seen, it is the first occurrence:
     • Add it to seen: seen.add(i).
     • Append it to result: result.append(i).
   • If i is already in seen, skip it.

3. Return the result list, which now holds each unique element in the order of its first appearance.

Walk‑through with the example [1, 2, 2, 3, 1, 4]

Final result: [1, 2, 3, 4].