Update bitonic_sort with type hints, doctest, snake_case names (#4016)

* Updated input
* Fix pre-commit error
* Add type hints, doctests, black, snake_case

Co-authored-by: Dhruv Manilawala <dhruvmanila@gmail.com>

sorts/bitonic_sort.py

@@ -1,58 +1,96 @@
-# Python program for Bitonic Sort. Note that this program
-# works only when size of input is a power of 2.
+"""
+Python program for Bitonic Sort.
+
+Note that this program works only when size of input is a power of 2.
+"""
+from typing import List
 
 
-# The parameter dir indicates the sorting direction, ASCENDING
-# or DESCENDING; if (a[i] > a[j]) agrees with the direction,
-# then a[i] and a[j] are interchanged.
-def compAndSwap(a, i, j, dire):
-    if (dire == 1 and a[i] > a[j]) or (dire == 0 and a[i] < a[j]):
-        a[i], a[j] = a[j], a[i]
+def comp_and_swap(array: List[int], index1: int, index2: int, direction: int) -> None:
+    """Compare the value at given index1 and index2 of the array and swap them as per
+    the given direction.
 
-        # It recursively sorts a bitonic sequence in ascending order,
+    The parameter direction indicates the sorting direction, ASCENDING(1) or
+    DESCENDING(0); if (a[i] > a[j]) agrees with the direction, then a[i] and a[j] are
+    interchanged.
+
+    >>> arr = [12, 42, -21, 1]
+    >>> comp_and_swap(arr, 1, 2, 1)
+    >>> print(arr)
+    [12, -21, 42, 1]
+
+    >>> comp_and_swap(arr, 1, 2, 0)
+    >>> print(arr)
+    [12, 42, -21, 1]
+
+    >>> comp_and_swap(arr, 0, 3, 1)
+    >>> print(arr)
+    [1, 42, -21, 12]
+
+    >>> comp_and_swap(arr, 0, 3, 0)
+    >>> print(arr)
+    [12, 42, -21, 1]
+    """
+    if (direction == 1 and array[index1] > array[index2]) or (
+        direction == 0 and array[index1] < array[index2]
+    ):
+        array[index1], array[index2] = array[index2], array[index1]
 
 
-# if dir = 1, and in descending order otherwise (means dir=0).
-# The sequence to be sorted starts at index position low,
-# the parameter cnt is the number of elements to be sorted.
-def bitonic_merge(a, low, cnt, dire):
-    if cnt > 1:
-        k = int(cnt / 2)
-        for i in range(low, low + k):
-            compAndSwap(a, i, i + k, dire)
-        bitonic_merge(a, low, k, dire)
-        bitonic_merge(a, low + k, k, dire)
+def bitonic_merge(array: List[int], low: int, length: int, direction: int) -> None:
+    """
+    It recursively sorts a bitonic sequence in ascending order, if direction = 1, and in
+    descending if direction = 0.
+    The sequence to be sorted starts at index position low, the parameter length is the
+    number of elements to be sorted.
 
-        # This function first produces a bitonic sequence by recursively
+    >>> arr = [12, 42, -21, 1]
+    >>> bitonic_merge(arr, 0, 4, 1)
+    >>> print(arr)
+    [-21, 1, 12, 42]
+
+    >>> bitonic_merge(arr, 0, 4, 0)
+    >>> print(arr)
+    [42, 12, 1, -21]
+    """
+    if length > 1:
+        middle = int(length / 2)
+        for i in range(low, low + middle):
+            comp_and_swap(array, i, i + middle, direction)
+        bitonic_merge(array, low, middle, direction)
+        bitonic_merge(array, low + middle, middle, direction)
 
 
-# sorting its two halves in opposite sorting orders, and then
-# calls bitonic_merge to make them in the same order
-def bitonic_sort(a, low, cnt, dire):
-    if cnt > 1:
-        k = int(cnt / 2)
-        bitonic_sort(a, low, k, 1)
-        bitonic_sort(a, low + k, k, 0)
-        bitonic_merge(a, low, cnt, dire)
+def bitonic_sort(array: List[int], low: int, length: int, direction: int) -> None:
+    """
+    This function first produces a bitonic sequence by recursively sorting its two
+    halves in opposite sorting orders, and then calls bitonic_merge to make them in the
+    same order.
 
-        # Caller of bitonic_sort for sorting the entire array of length N
+    >>> arr = [12, 34, 92, -23, 0, -121, -167, 145]
+    >>> bitonic_sort(arr, 0, 8, 1)
+    >>> arr
+    [-167, -121, -23, 0, 12, 34, 92, 145]
 
-
-# in ASCENDING order
-def sort(a, N, up):
-    bitonic_sort(a, 0, N, up)
+    >>> bitonic_sort(arr, 0, 8, 0)
+    >>> arr
+    [145, 92, 34, 12, 0, -23, -121, -167]
+    """
+    if length > 1:
+        middle = int(length / 2)
+        bitonic_sort(array, low, middle, 1)
+        bitonic_sort(array, low + middle, middle, 0)
+        bitonic_merge(array, low, length, direction)
 
 
 if __name__ == "__main__":
+    user_input = input("Enter numbers separated by a comma:\n").strip()
+    unsorted = [int(item.strip()) for item in user_input.split(",")]
 
-    a = []
+    bitonic_sort(unsorted, 0, len(unsorted), 1)
+    print("\nSorted array in ascending order is: ", end="")
+    print(*unsorted, sep=", ")
 
-    n = int(input().strip())
-    for i in range(n):
-        a.append(int(input().strip()))
-    up = 1
-
-    sort(a, n, up)
-    print("\n\nSorted array is")
-    for i in range(n):
-        print("%d" % a[i])
+    bitonic_merge(unsorted, 0, len(unsorted), 0)
+    print("Sorted array in descending order is: ", end="")
+    print(*unsorted, sep=", ")