Create quicksort.py

divide_and_conquer/quicksort.py

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+def quicksort(arr: list) -> list:
+    """Quicksort function implementation in Python.
+
+    https://en.wikipedia.org/wiki/Quicksort
+    >>> quicksort([])
+    []
+    >>> quicksort([5])
+    [5]
+    >>> quicksort([3, 6, 8, 10, 1, 2, 1, 3, 2, 8])
+    [1, 1, 2, 2, 3, 3, 6, 8, 8, 10]
+    """
+
+    # If the length of the array is less than or equal to 1, then there's
+    # nothing to sort, so return the given array
+    if len(arr) <= 1:
+        return arr
+
+    # In quicksort a element needs to be selected as pivot, it can be anywhere
+    # In this case let the pivot be the first element
+    pivot = arr[0]
+
+    # Using list comprehension creating three list object: smaller_elemnts,
+    # pivot_elements & larger_elements
+    # based on the comparison with the pivot element
+    smaller_elements = [x for x in arr if x < pivot]
+    pivot_elements = [x for x in arr if x == pivot]
+    larger_elements = [x for x in arr if x > pivot]
+
+    # Recursively splitting the list object to determine the correct
+    # position of the element
+    return quicksort(smaller_elements) + pivot_elements + quicksort(larger_elements)
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()