Sleep sort

Author: Sai Rahul Guggilam

sorts/sleep_sort.py

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+"""
+An implementation of Sleep Sort.
+
+Description
+-----------
+Sleep Sort is a highly unconventional algorithm that leverages timing delays
+to produce a sorted sequence. Each element in the array is assigned to a thread
+that sleeps for a duration proportional to its value. As threads "wake up,"
+they output numbers in increasing order.
+
+This algorithm only works for non-negative integers and is non-deterministic
+in real systems due to thread scheduling and timing inaccuracies.
+
+Time complexity: O(n) expected (but unreliable in practice)
+Space complexity: O(n) for thread management
+"""
+
+import threading
+import time
+from typing import List
+
+
+def sleep_sort(arr: List[int]) -> List[int]:
+    """
+    Sorts a list of non-negative integers using the Sleep Sort algorithm.
+
+    Parameters
+    ----------
+    arr : List[int]
+        A list of non-negative integers to be sorted.
+
+    Returns
+    -------
+    List[int]
+        A new list containing the elements in sorted order.
+
+    Example
+    -------
+    >>> sleep_sort([3, 1, 2])
+    [1, 2, 3]
+    """
+    if not arr:
+        return []
+
+    result: List[int] = []
+    threads = []
+
+    def _sleep_and_append(n: int) -> None:
+        """Sleeps for n * 0.01 seconds and appends n to the result."""
+        time.sleep(n * 0.01)
+        result.append(n)
+
+    for num in arr:
+        if num < 0:
+            raise ValueError("Sleep Sort only supports non-negative integers.")
+        thread = threading.Thread(target=_sleep_and_append, args=(num,))
+        threads.append(thread)
+        thread.start()
+
+    for thread in threads:
+        thread.join()
+
+    return result
+
+
+def _test() -> None:
+    """Basic test cases for sleep_sort."""
+    test_cases = [
+        [],
+        [1],
+        [3, 1, 2],
+        [0, 0, 1],
+        [5, 3, 9, 1, 4],
+    ]
+
+    for case in test_cases:
+        sorted_case = sorted(case)
+        assert sleep_sort(case) == sorted_case, f"Failed on {case}"
+    print("All tests passed.")
+
+
+if __name__ == "__main__":
+    _test()