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Space- Yieni #15

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17 changes: 15 additions & 2 deletions lib/heap_sort.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -4,5 +4,18 @@
# Time Complexity: ?
# Space Complexity: ?
def heapsort(list)
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@CheezItMan CheezItMan Sep 28, 2020

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👍 Time & Space complexity?

raise NotImplementedError, "Method not implemented yet..."
end
return list if list.empty? || list.length == 1

heap = MinHeap.new

list.each do |num|
heap.add(num)
end
list = []
until heap.empty?
removed = heap.remove
list << removed
end
return list
end

68 changes: 61 additions & 7 deletions lib/min_heap.rb
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Expand Up @@ -14,21 +14,33 @@ def initialize
end

# This method adds a HeapNode instance to the heap
# Time Complexity: ?
# Space Complexity: ?
# Time Complexity: 0(1)?
# Space Complexity: o(n)?
def add(key, value = key)
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@CheezItMan CheezItMan Sep 28, 2020

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👍 The time complexity would be O(log n) because of how you heap_up going up through the levels of the tree.

Similarly because heap_up is recursive the time complexity is O(log n).

raise NotImplementedError, "Method not implemented yet..."
node = HeapNode.new(key, value)
if @store.empty?
@store << node
else
@store << node
current_index = @store.length - 1
@store = heap_up(current_index)
end

end

# This method removes and returns an element from the heap
# maintaining the heap structure
# Time Complexity: ?
# Space Complexity: ?
def remove()
Comment on lines 33 to 35
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@CheezItMan CheezItMan Sep 28, 2020

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👍 Time & space complexity?

raise NotImplementedError, "Method not implemented yet..."
removed = @store[0].value
@store[0] = @store[@store.length - 1]
parent_node = @store[0]
@store.pop
@store = heap_down(0)
return removed
end


# Used for Testing
def to_s
return "[]" if @store.empty?
Expand All @@ -47,7 +59,7 @@ def to_s
# Time complexity: ?
# Space complexity: ?
def empty?
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👍

raise NotImplementedError, "Method not implemented yet..."
return @store.empty?
end

private
Expand All @@ -58,14 +70,56 @@ def empty?
# Time complexity: ?
# Space complexity: ?
def heap_up(index)
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👍 Time & space complexity?

node = @store[index]
parent_index = (index - 1)/2
parent_node = @store[parent_index]
return @store if parent_node.key <= node.key || index == 0

@store[index] = parent_node
@store[parent_index] = node

index = parent_index
return heap_up(index)
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)
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@CheezItMan CheezItMan Sep 28, 2020

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This works, but you've overcomplicated some of the if statements.

raise NotImplementedError, "Method not implemented yet..."
parent_node = @store[index]
left_child_index = index * 2 + 1
right_child_index = index * 2 + 2
left_child = @store[left_child_index]
right_child = @store[right_child_index]
if left_child.nil? == false && right_child.nil? == false
return @store if (parent_node.key <= left_child.key && parent_node.key <= right_child.key)

if left_child.key < right_child.key
@store[index] = left_child
@store[left_child_index] = parent_node
index = left_child_index
return heap_down(index)
else
@store[index] = right_child
@store[right_child_index] = parent_node
index = right_child_index
return heap_down(index)
end
elsif left_child.nil? == true && right_child.nil? == true
return @store
elsif left_child.nil? == true && right_child.nil? == false
Comment on lines +108 to +110
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@CheezItMan CheezItMan Sep 28, 2020

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I don't think the right child can't be nil if the left child is.

similarly I don't think the left child can be nil and the right not nil.

return @store if parent_node.key <= right_child.key
@store[index] = right_child
@store[right_child_index] = parent_node
index = right_child_index
return heap_down(index)
else left_child.nil? == false && right_child.nil? == true
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Good catch checking if the right child is past the end of the array and the left isn't.

return @store if parent_node.key <= left_child.key
@store[index] = left_child
@store[left_child_index] = parent_node
index = left_child_index
return heap_down(index)
end
end

# If you want a swap method... you're welcome
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2 changes: 1 addition & 1 deletion test/heapsort_test.rb
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Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
require_relative "test_helper"

xdescribe "heapsort" do
describe "heapsort" do
it "sorts an empty array" do
# Arrange
list = []
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1 change: 0 additions & 1 deletion test/min_heap_test.rb
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Expand Up @@ -47,7 +47,6 @@
output = heap.to_s

# Assert

expect(output).must_equal "[Donuts, Pizza, Pasta, Soup, Cookies, Cake]"
end

Expand Down