Added Quick Sort Program

divide_and_conquer/quicksort.py

@@ -0,0 +1,69 @@
+from __future__ import annotations
+
+def partition(array: list, start: int, end: int) -> int:
+    """Helper function for Quick Sort.
+
+    >>> array = [5, 8, 3, 2, 9, 6]
+    >>> start = 0
+    >>> end = 5
+    >>> index = partition(array, start, end)
+    >>> index  # The pivot index
+    3
+    >>> sorted(array[:index])  # Elements less than pivot
+    [2, 3, 5]
+    >>> sorted(array[index+1:])  # Elements greater than pivot
+    [8, 9]
+
+    >>> array = []
+    >>> start = 0
+    >>> end = 0
+    >>> partition(array, start, end)
+    0
+    >>> array
+    []
+    """
+    if not array: 
+        return 0
+    pivot = array[end]
+    index = start - 1
+    for j in range(start, end):
+        if array[j] <= pivot:
+            index += 1
+            array[index], array[j] = array[j], array[index]
+    array[index+1], array[end] = array[end], array[index+1]
+    return index+1
+
+def quicksort(array, start, end):
+    """Returns a list of sorted array elements using Quick Sort.
+
+    >>> from random import shuffle
+    >>> array = [5, 8, 3, 2, 9, 6]
+    >>> start = 0
+    >>> end = 5
+    >>> quicksort(array, start, end)
+    >>> array
+    [2, 3, 5, 6, 8, 9]
+
+    >>> shuffle(array)
+    >>> quicksort(array, start, end)
+    >>> array
+    [2, 3, 5, 6, 8, 9]
+
+    >>> array = [-100]
+    >>> quicksort(array, 0, len(array) - 1)
+    >>> array
+    [-100]
+
+    >>> array = []
+    >>> quicksort(array, 0, 0)
+    >>> array
+    []
+    """
+    if start < end:
+        partition_index = partition(array, start, end)
+        quicksort(array, start, partition_index-1)
+        quicksort(array, partition_index+1, end)
+
+if __name__ == "__main__":
+    import doctest
+    doctest.testmod()