heap_sort.py

# Python program for implementation of heap Sort 

# To heapify subtree rooted at index i. 
# n is size of heap 
def heapify(arr, n, i): 
	largest = i # Initialize largest as root 
	l = 2 * i + 1	 # left = 2*i + 1 
	r = 2 * i + 2	 # right = 2*i + 2 

	# See if left child of root exists and is 
	# greater than root 
	if l < n and arr[i] < arr[l]: 
		largest = l 

	# See if right child of root exists and is 
	# greater than root 
	if r < n and arr[largest] < arr[r]: 
		largest = r 

	# Change root, if needed 
	if largest != i: 
		arr[i],arr[largest] = arr[largest],arr[i] # swap 

		# Heapify the root. 
		heapify(arr, n, largest) 

# The main function to sort an array of given size 
def heapSort(arr): 
	n = len(arr) 

	# Build a maxheap. 
	for i in range(n, -1, -1): 
		heapify(arr, n, i) 

	# One by one extract elements 
	for i in range(n-1, 0, -1): 
		arr[i], arr[0] = arr[0], arr[i] # swap 
		heapify(arr, i, 0) 

if __name__ == "__main__":
	# Driver code to test above 
	arr = [ 12, 11, 13, 5, 6, 7] 
	heapSort(arr) 
	n = len(arr) 
	print ("Sorted array is") 
	for i in range(n): 
		print ("%d" %arr[i]),