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Task/Sorting-algorithms-Heapsort/Python/sorting-algorithms-heapsort.py

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+def heapsort(lst):
+  ''' Heapsort. Note: this function sorts in-place (it mutates the list). '''
+
+  # in pseudo-code, heapify only called once, so inline it here
+  for start in range((len(lst)-2)/2, -1, -1):
+    siftdown(lst, start, len(lst)-1)
+
+  for end in range(len(lst)-1, 0, -1):
+    lst[end], lst[0] = lst[0], lst[end]
+    siftdown(lst, 0, end - 1)
+  return lst
+
+def siftdown(lst, start, end):
+  root = start
+  while True:
+    child = root * 2 + 1
+    if child > end: break
+    if child + 1 <= end and lst[child] < lst[child + 1]:
+      child += 1
+    if lst[root] < lst[child]:
+      lst[root], lst[child] = lst[child], lst[root]
+      root = child
+    else:
+      break