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Useful Heap Methods
Heapq
We often need to find the largest and smallest values in a list. We can use heapq to accomplish this easily.
How to get the five largest numbers from this list?
nums = [99, 54, 12, 47, 41, 23, 45, 43, 37, 98, 100, 101]
heapq.nlargest(k, nums)
to find largest values
Use import heapq
nums = [99, 54, 12, 47, 41, 23, 45, 43, 37, 98, 100, 101]
a, b, c, d, e = heapq.nlargest(5, nums)
print(a, b, c, d, e)
# 101 100 99 98 54
heapq.nsmallest(k, nums)
to find smallest values
Use nums = [99, 54, 12, 47, 41, 23, 45, 43, 37, 98, 100, 101]
a, b, c, d, e = heapq.nsmallest(5, nums)
print(a, b, c, d, e)
# 12 23 37 41 43
The return of both these methods are unpacked/destructured values.
heapq.heapify(nums)
will create a heap for us
Use nums = [99, 54, 12, 47, 41, 23, 45, 43, 37, 98, 100, 101]
heapq.heapify(nums)
print(nums)
# [12, 37, 23, 43, 41, 99, 45, 54, 47, 98, 100, 101]
Create a heap
By default python creates a min heap, a heap with the smallest values first(at the root).
heap = [10, 1, 2, 3, 4, 5]
heapq.heapify(heap)
print(heap[0]) # 1
heapq.heappop(heap)
print(heap[0]) # 2
Max Heap
The root has the largest values
import heapq
heap = [10, 1, 2, 3, 4, 5]
heapq._heapify_max(heap)
print(heap[0]) # 10
heapq._heappop_max(heap)
print(heap[0]) # 5
Print heap as a tree
def show_tree(tree, total_width=60, fill=' '):
"""Pretty-print a tree.
total_width depends on your input size"""
output = StringIO()
last_row = -1
for i, n in enumerate(tree):
if i:
row = int(math.floor(math.log(i+1, 2)))
else:
row = 0
if row != last_row:
output.write('\n')
columns = 2**row
col_width = int(math.floor((total_width * 1.0) / columns))
output.write(str(n).center(col_width, fill))
last_row = row
print(output.getvalue())
print('-' * total_width)
return