Bitonic Sort.py

# Python program for Bitonic Sort. Note that this program
# works only when size of input is a power of 2.

# 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]

# It recursively sorts a bitonic sequence in ascending order,
# 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 bitonicMerge(a, low, cnt, dire):
	if cnt > 1:
		k = cnt//2
		for i in range(low, low+k):
			compAndSwap(a, i, i+k, dire)
		bitonicMerge(a, low, k, dire)
		bitonicMerge(a, low+k, k, dire)

# This function first produces a bitonic sequence by recursively
# sorting its two halves in opposite sorting orders, and then
# calls bitonicMerge to make them in the same order


def bitonicSort(a, low, cnt, dire):
	if cnt > 1:
		k = cnt//2
		bitonicSort(a, low, k, 1)
		bitonicSort(a, low+k, k, 0)
		bitonicMerge(a, low, cnt, dire)

# Caller of bitonicSort for sorting the entire array of length N
# in ASCENDING order


def sort(a, N, up):
	bitonicSort(a, 0, N, up)


# Driver code to test above
a = [3, 7, 4, 8, 6, 2, 1, 5]
n = len(a)
up = 1

sort(a, n, up)
print("Sorted array is")
for i in range(n):
	print("%d" % a[i], end=" ")