Create slowsort.py

sorts/slowsort.py

@@ -0,0 +1,61 @@
+"""
+Slowsort is a sorting algorithm. It is of humorous nature and not useful.
+It's based on the principle of multiply and surrender,
+a tongue-in-cheek joke of divide and conquer.
+It was published in 1986 by Andrei Broder and Jorge Stolfi
+in their paper Pessimal Algorithms and Simplexity Analysis
+(a parody of optimal algorithms and complexity analysis).
+
+Source: https://en.wikipedia.org/wiki/Slowsort
+"""
+
+from typing import Optional
+
+
+def slowsort(sequence: list, i: Optional[int] = None, j: Optional[int] = None) -> None:
+    """
+    Sorts sequence[i..j] (both inclusive) in-place.
+    i defaults to 0 if not given.
+    j defaults to len(sequence) - 1 if not given.
+    It returns None.
+    >>> sequence = [1, 6, 2, 5, 3, 4, 4, 5]; slowsort(sequence); sequence
+    [1, 2, 3, 4, 4, 5, 5, 6]
+    >>> sequence = []; slowsort(sequence); sequence
+    []
+    >>> sequence = [2]; slowsort(sequence); sequence
+    [2]
+    >>> sequence = [1, 2, 3, 4]; slowsort(sequence); sequence
+    [1, 2, 3, 4]
+    >>> sequence = [4, 3, 2, 1]; slowsort(sequence); sequence
+    [1, 2, 3, 4]
+    >>> sequence = [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]; slowsort(sequence, 2, 7); sequence
+    [9, 8, 2, 3, 4, 5, 6, 7, 1, 0]
+    >>> sequence = [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]; slowsort(sequence, j = 4); sequence
+    [5, 6, 7, 8, 9, 4, 3, 2, 1, 0]
+    >>> sequence = [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]; slowsort(sequence, i = 5); sequence
+    [9, 8, 7, 6, 5, 0, 1, 2, 3, 4]
+    """
+    if i is None:
+        i = 0
+
+    if j is None:
+        j = len(sequence) - 1
+
+    if i >= j:
+        return
+
+    m = (i + j) // 2
+
+    slowsort(sequence, i, m)
+    slowsort(sequence, m + 1, j)
+
+    if sequence[j] < sequence[m]:
+        sequence[j], sequence[m] = sequence[m], sequence[j]
+
+    slowsort(sequence, i, j - 1)
+
+
+if __name__ == "__main__":
+    from doctest import testmod
+
+    testmod()