Python-Programming-Exercises-by-EKIKA/list.md

Python List Exercises

These exercises will help you get really good at using lists in Python. You'll practice things like loops, slicing, grouping, and working with nested lists.

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Exercise 1

Flatten a Nested List

Problem

Write a function flatten_list(nested_list) that takes a list which may contain nested lists of any depth, and returns a single, flat list.

Example

flatten_list([1, [2, 3], [4, [5, 6], 7]])
# Output: [1, 2, 3, 4, 5, 6, 7]

Concepts

• Recursion
• isinstance type checking
• extend vs append

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Exercise 2

Group Consecutive Duplicates

Problem

Write a function group_consecutive(lst) that groups consecutive identical elements into sublists.

Example

group_consecutive([1, 1, 2, 2, 2, 3, 1, 1])
# Output: [[1, 1], [2, 2, 2], [3], [1, 1]]

Concepts

• Iteration with state tracking
• Temporary sublists
• for loops with conditionals

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Exercise 3

Rotate List k Times

Problem

Write a function rotate_list(lst, k) that rotates the list right by k steps.

BONUS: Support negative k to rotate left.

Example

rotate_list([1, 2, 3, 4, 5], 2)
# Output: [4, 5, 1, 2, 3]

Concepts

• Identify concepts yourself.

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Exercise 4

List Difference by Value and Order

Problem

Write a function diff_lists(a, b) that removes each occurrence in b from a, respecting the number of times elements occur.

Example

diff_lists([1, 2, 2, 3, 4], [2, 4])
# Output: [1, 2, 3]

One 2 and the 4 are removed. The second 2 remains.

Concepts

• Element-by-element removal
• List copying
• in with deletion logic

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✅ Pro Tips

• Try solving without using libraries.

• Then try versions using collections.Counter, itertools, or functools for practice.

• Write unit tests for edge cases:

  • Empty lists
  • Deep nesting
  • Large k values
  • Negative numbers