Create quicksort.py

divide_and_conquer/quicksort.py

@@ -0,0 +1,68 @@
+from __future__ import annotations
+
+def partition(array: list, low: int, high: int) -> int:
+    """Helper function for quicksort to partition the array.
+
+    >>> array = [3, 2, 1]
+    >>> partition(array, 0, len(array) - 1)
+    0
+    >>> array
+    [1, 2, 3]
+
+    >>> array = [12, 4, 5, 2, 3]
+    >>> idx = partition(array, 0, len(array) - 1)
+    >>> array[:idx], array[idx], array[idx+1:]
+    ([2, 3, 4], 5, [12])
+    """
+    pivot = array[high]
+    i = low - 1  # Pointer for the smaller element
+
+    for j in range(low, high):
+        if array[j] <= pivot:
+            i += 1
+            array[i], array[j] = array[j], array[i]
+
+    array[i + 1], array[high] = array[high], array[i + 1]
+    return i + 1
+
+def quicksort(array: list, low: int = 0, high: int | None = None) -> list:
+    """Returns a sorted list using the quicksort algorithm.
+
+    >>> from random import shuffle
+    >>> array = [-2, 3, -10, 11, 99, 100000, 100, -200]
+    >>> shuffle(array)
+    >>> quicksort(array)
+    [-200, -10, -2, 3, 11, 99, 100, 100000]
+
+    >>> shuffle(array)
+    >>> quicksort(array)
+    [-200, -10, -2, 3, 11, 99, 100, 100000]
+
+    >>> quicksort([-200])
+    [-200]
+
+    >>> array = [-2, 3, -10, 11, 99, 100000, 100, -200]
+    >>> shuffle(array)
+    >>> sorted(array) == quicksort(array)
+    True
+
+    >>> quicksort([])
+    []
+
+    >>> array = [10000000, 1, -1111111111, 101111111112, 9000002]
+    >>> sorted(array) == quicksort(array)
+    True
+    """
+    if high is None:
+        high = len(array) - 1
+
+    if low < high:
+        pivot_index = partition(array, low, high)
+        quicksort(array, low, pivot_index - 1)
+        quicksort(array, pivot_index + 1, high)
+
+    return array
+
+if __name__ == "__main__":
+    import doctest
+    doctest.testmod()