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Ida - Fire #34

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19 changes: 15 additions & 4 deletions lib/heap_sort.rb
Original file line number Diff line number Diff line change
@@ -1,8 +1,19 @@

require_relative "./min_heap"

# This method uses a heap to sort an array.
# Time Complexity: ?
# Space Complexity: ?
# Time Complexity: o(log n)
# Space Complexity: o(n)
def heap_sort(list)
raise NotImplementedError, "Method not implemented yet..."
heap = MinHeap.new

list.each do |item|
heap.add(item)
end

sorted_list = []
until heap.empty?
sorted_list << heap.remove
end

return sorted_list
end
66 changes: 53 additions & 13 deletions lib/min_heap.rb
Original file line number Diff line number Diff line change
Expand Up @@ -14,18 +14,29 @@ def initialize
end

# This method adds a HeapNode instance to the heap
# Time Complexity: ?
# Space Complexity: ?
# Time Complexity: o(log n)
# Space Complexity: o(n)
def add(key, value = key)
raise NotImplementedError, "Method not implemented yet..."

new_node = HeapNode.new(key, value)
@store.push(new_node)

heap_up(@store.length - 1)

end

# This method removes and returns an element from the heap
# maintaining the heap structure
# Time Complexity: ?
# Space Complexity: ?
# Time Complexity: o(log n)
# Space Complexity: o(log n)
def remove()
raise NotImplementedError, "Method not implemented yet..."

return if @store.empty?

swap(0, @store.length - 1)
removed_result = @store.pop
heap_down(0) unless @store.empty?
return removed_result.value
end


Expand All @@ -44,28 +55,57 @@ def to_s
end

# This method returns true if the heap is empty
# Time complexity: ?
# Space complexity: ?
# Time complexity: o(1)
# Space complexity: o(1)
def empty?
raise NotImplementedError, "Method not implemented yet..."
return @store.empty?
end

private

# This helper method takes an index and
# moves it up the heap, if it is less than it's parent node.
# It could be **very** helpful for the add method.
# Time complexity: ?
# Space complexity: ?
# Time complexity: o(log n)
# Space complexity: o(log n)
def heap_up(index)

return if index == 0

parent = (index - 1) / 2
if @store[parent].key > @store[index].key
swap(parent, index)
heap_up(parent)
else
return
end
end

# This helper method takes an index and
# moves it up the heap if it's smaller
# than it's parent node.
def heap_down(index)
raise NotImplementedError, "Method not implemented yet..."
left_index = index * 2 + 1
right_index = index * 2 + 2
return if left_index >= @store.length
child = nil
left = @store[left_index]
right = @store[right_index]
if left && right
child = left.key < right.key ? left_index : right_index
if @store[child].key < @store[index].key
swap(index, child)
index = child
else
return
end
elsif left && !right
return unless left.key < @store[index].key
child = left_index
swap(index, child)
index = child
else
return
end
end

# If you want a swap method... you're welcome
Expand Down
8 changes: 4 additions & 4 deletions test/heapsort_test.rb
Original file line number Diff line number Diff line change
@@ -1,12 +1,12 @@
require_relative "test_helper"

xdescribe "heapsort" do
describe "heapsort" do
it "sorts an empty array" do
# Arrange
list = []

# Act
result = heapsort(list)
result = heap_sort(list)

# Assert
expect(result).must_equal []
Expand All @@ -17,7 +17,7 @@
list = [5]

# Act
result = heapsort(list)
result = heap_sort(list)

# Assert
expect(result).must_equal [5]
Expand All @@ -28,7 +28,7 @@
list = [5, 27, 3, 16, -50]

# Act
result = heapsort(list)
result = heap_sort(list)

# Assert
expect(result).must_equal [-50, 3, 5, 16, 27]
Expand Down