mirror of
https://github.com/TheAlgorithms/Python.git
synced 2024-11-27 15:01:08 +00:00
bc8df6de31
* [pre-commit.ci] pre-commit autoupdate updates: - [github.com/astral-sh/ruff-pre-commit: v0.2.2 → v0.3.2](https://github.com/astral-sh/ruff-pre-commit/compare/v0.2.2...v0.3.2) - [github.com/pre-commit/mirrors-mypy: v1.8.0 → v1.9.0](https://github.com/pre-commit/mirrors-mypy/compare/v1.8.0...v1.9.0) * [pre-commit.ci] auto fixes from pre-commit.com hooks for more information, see https://pre-commit.ci --------- Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
99 lines
3.6 KiB
Python
99 lines
3.6 KiB
Python
"""
|
|
A pure implementation of Dutch national flag (DNF) sort algorithm in Python.
|
|
Dutch National Flag algorithm is an algorithm originally designed by Edsger Dijkstra.
|
|
It is the most optimal sort for 3 unique values (eg. 0, 1, 2) in a sequence. DNF can
|
|
sort a sequence of n size with [0 <= a[i] <= 2] at guaranteed O(n) complexity in a
|
|
single pass.
|
|
|
|
The flag of the Netherlands consists of three colors: white, red, and blue.
|
|
The task is to randomly arrange balls of white, red, and blue in such a way that balls
|
|
of the same color are placed together. DNF sorts a sequence of 0, 1, and 2's in linear
|
|
time that does not consume any extra space. This algorithm can be implemented only on
|
|
a sequence that contains three unique elements.
|
|
|
|
1) Time complexity is O(n).
|
|
2) Space complexity is O(1).
|
|
|
|
More info on: https://en.wikipedia.org/wiki/Dutch_national_flag_problem
|
|
|
|
For doctests run following command:
|
|
python3 -m doctest -v dutch_national_flag_sort.py
|
|
|
|
For manual testing run:
|
|
python dnf_sort.py
|
|
"""
|
|
|
|
# Python program to sort a sequence containing only 0, 1 and 2 in a single pass.
|
|
red = 0 # The first color of the flag.
|
|
white = 1 # The second color of the flag.
|
|
blue = 2 # The third color of the flag.
|
|
colors = (red, white, blue)
|
|
|
|
|
|
def dutch_national_flag_sort(sequence: list) -> list:
|
|
"""
|
|
A pure Python implementation of Dutch National Flag sort algorithm.
|
|
:param data: 3 unique integer values (e.g., 0, 1, 2) in an sequence
|
|
:return: The same collection in ascending order
|
|
|
|
>>> dutch_national_flag_sort([])
|
|
[]
|
|
>>> dutch_national_flag_sort([0])
|
|
[0]
|
|
>>> dutch_national_flag_sort([2, 1, 0, 0, 1, 2])
|
|
[0, 0, 1, 1, 2, 2]
|
|
>>> dutch_national_flag_sort([0, 1, 1, 0, 1, 2, 1, 2, 0, 0, 0, 1])
|
|
[0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 2, 2]
|
|
>>> dutch_national_flag_sort("abacab")
|
|
Traceback (most recent call last):
|
|
...
|
|
ValueError: The elements inside the sequence must contains only (0, 1, 2) values
|
|
>>> dutch_national_flag_sort("Abacab")
|
|
Traceback (most recent call last):
|
|
...
|
|
ValueError: The elements inside the sequence must contains only (0, 1, 2) values
|
|
>>> dutch_national_flag_sort([3, 2, 3, 1, 3, 0, 3])
|
|
Traceback (most recent call last):
|
|
...
|
|
ValueError: The elements inside the sequence must contains only (0, 1, 2) values
|
|
>>> dutch_national_flag_sort([-1, 2, -1, 1, -1, 0, -1])
|
|
Traceback (most recent call last):
|
|
...
|
|
ValueError: The elements inside the sequence must contains only (0, 1, 2) values
|
|
>>> dutch_national_flag_sort([1.1, 2, 1.1, 1, 1.1, 0, 1.1])
|
|
Traceback (most recent call last):
|
|
...
|
|
ValueError: The elements inside the sequence must contains only (0, 1, 2) values
|
|
"""
|
|
if not sequence:
|
|
return []
|
|
if len(sequence) == 1:
|
|
return list(sequence)
|
|
low = 0
|
|
high = len(sequence) - 1
|
|
mid = 0
|
|
while mid <= high:
|
|
if sequence[mid] == colors[0]:
|
|
sequence[low], sequence[mid] = sequence[mid], sequence[low]
|
|
low += 1
|
|
mid += 1
|
|
elif sequence[mid] == colors[1]:
|
|
mid += 1
|
|
elif sequence[mid] == colors[2]:
|
|
sequence[mid], sequence[high] = sequence[high], sequence[mid]
|
|
high -= 1
|
|
else:
|
|
msg = f"The elements inside the sequence must contains only {colors} values"
|
|
raise ValueError(msg)
|
|
return sequence
|
|
|
|
|
|
if __name__ == "__main__":
|
|
import doctest
|
|
|
|
doctest.testmod()
|
|
|
|
user_input = input("Enter numbers separated by commas:\n").strip()
|
|
unsorted = [int(item.strip()) for item in user_input.split(",")]
|
|
print(f"{dutch_national_flag_sort(unsorted)}")
|