Jak wykonywać heap w Pythonie?
"""
The below code provides an implementation
for the heap sort algorithm
(https://en.wikipedia.org/wiki/Heapsort).
Sorting a list via heap sort is a two-step
process:
1. In first step, transform the original list
into a heap.
2. In second step, sort the list by placing
the values in order at end of list.
Let n be the number of elements in list to sort.
Time complexity: O(nlog2(n))
Space complexity: O(1), sorting is done in place.
"""
from heapq import heapify
def heap_sort(list):
n = len(list)
# First step: turn list into a heap
heapify(list)
print(list)
# Second step: repeatedly place next
# smallest value at end of the list
for idx in range(n-1, 0, -1):
swap(0, idx, list)
bubble_down(0, idx-1, list)
def swap(idx1, idx2, list):
list[idx1], list[idx2] = list[idx2], list[idx1]
def bubble_down(current_idx, last_idx, heap):
# Method used to restore heap order property when violated
child_one_idx = current_idx * 2 + 1
while child_one_idx <= last_idx:
child_two_idx = current_idx * 2 + 2 if current_idx*2 + 2 <= last_idx else -1
if child_two_idx > -1 and heap[child_two_idx] < heap[child_one_idx]:
idx_to_swap = child_two_idx
else:
idx_to_swap = child_one_idx
if heap[idx_to_swap] < heap[current_idx]:
swap(current_idx, idx_to_swap, heap)
current_idx = idx_to_swap
child_one_idx = current_idx * 2 + 1
else:
return
list = [1, 10, 4, 3, 2]
heap_sort(list)
# Descending order
print(list) # [10, 4, 3, 2, 1]
# Ascending order
list.reverse()
print(list) # [1, 2, 3, 4, 10]
Wissam