programming-for-dummies

400
Using Heap Sort
The two criteria for storing data in a heap are that
✦ Every parent node must contain a value greater than either of its
child nodes.
✦ The tree must fill each level before adding nodes to the next lower level.
If there aren’t enough nodes to fill out an entire level, the nodes must fill
out as much of the last level as possible, starting from the left.
Figure 1-6 shows a valid heap and two invalid heaps.
The heap sort algorithm works like this:
1. Store an unsorted list in a heap data structure, which sorts data so the
highest values appear near the top of the heap.
2. Yank off the highest value stored in the root node and store this value
as the end of the sorted list.
3. Re-sort the heap so the highest values appear near the top of the heap.
4. Repeat Steps 2 and 3 until all values have been removed from the
heap and sorted.
94
32
46 74 Levels
46
9
21
32
50
68
21
94
50
68
9
A heap
74
Not a heap since not every
parent node value is greater
than its child node values.
32
Figure 1-6:
Valid and
invalid heap
binary trees.
74
21
46
94
50
9
68
Not a heap since earlier
levels are not full.