Create stalin_sort.py

sorts/stalin_sort.py

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+"""
+Stalin Sort algorithm: Removes elements that are out of order.
+Elements that are not greater than or equal to the previous element are discarded.
+Reference: https://medium.com/@kaweendra/the-ultimate-sorting-algorithm-6513d6968420
+"""
+
+
+def stalin_sort(sequence: list[int]) -> list[int]:
+    """
+    Sorts a list using the Stalin sort algorithm.
+
+    >>> stalin_sort([4, 3, 5, 2, 1, 7])
+    [4, 5, 7]
+
+    >>> stalin_sort([1, 2, 3, 4])
+    [1, 2, 3, 4]
+
+    >>> stalin_sort([4, 5, 5, 2, 3])
+    [4, 5, 5]
+
+    >>> stalin_sort([6, 11, 12, 4, 1, 5])
+    [6, 11, 12]
+
+    >>> stalin_sort([5, 0, 4, 3])
+    [5]
+
+    >>> stalin_sort([5, 4, 3, 2, 1])
+    [5]
+
+    >>> stalin_sort([1, 2, 3, 4, 5])
+    [1, 2, 3, 4, 5]
+
+    >>> stalin_sort([1, 2, 8, 7, 6])
+    [1, 2, 8]
+    """
+    if any(x < 0 for x in sequence):
+        raise ValueError("Sequence must only contain non-negative integers")
+
+    result = [sequence[0]]
+    for i in range(1, len(sequence)):
+        if sequence[i] >= result[-1]:
+            result.append(sequence[i])
+
+    return result
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()