Class: Timers::PriorityHeap
- Inherits:
-
Object
- Object
- Timers::PriorityHeap
- Defined in:
- lib/timers/priority_heap.rb
Overview
A priority queue implementation using a standard binary minheap. It uses straight comparison of its contents to determine priority. This works because a Handle from Timers::Events implements the ‘<’ operation by comparing the expiry time. See <en.wikipedia.org/wiki/Binary_heap> for explanations of the main methods.
Instance Method Summary collapse
-
#initialize ⇒ PriorityHeap
constructor
A new instance of PriorityHeap.
-
#peek ⇒ Object
Returns the earliest timer or nil if the heap is empty.
-
#pop ⇒ Object
Returns the earliest timer if the heap is non-empty and removes it from the heap.
-
#push(element) ⇒ Object
Inserts a new timer into the heap, then rearranges elements until the heap invariant is true again.
-
#size ⇒ Object
Returns the number of elements in the heap.
Constructor Details
#initialize ⇒ PriorityHeap
Returns a new instance of PriorityHeap.
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# File 'lib/timers/priority_heap.rb', line 30 def initialize # The heap is represented with an array containing a binary tree. See # https://en.wikipedia.org/wiki/Binary_heap#Heap_implementation for how this array # is built up. @contents = [] end |
Instance Method Details
#peek ⇒ Object
Returns the earliest timer or nil if the heap is empty.
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# File 'lib/timers/priority_heap.rb', line 38 def peek @contents[0] end |
#pop ⇒ Object
Returns the earliest timer if the heap is non-empty and removes it from the heap. Returns nil if the heap is empty. (and doesn’t change the heap in that case)
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# File 'lib/timers/priority_heap.rb', line 49 def pop # If the heap is empty: if @contents.empty? return nil end # If we have only one item, no swapping is required: if @contents.size == 1 return @contents.pop end # Take the root of the tree: value = @contents[0] # Remove the last item in the tree: last = @contents.pop # Overwrite the root of the tree with the item: @contents[0] = last # Bubble it down into place: bubble_down(0) # validate! return value end |
#push(element) ⇒ Object
Inserts a new timer into the heap, then rearranges elements until the heap invariant is true again.
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# File 'lib/timers/priority_heap.rb', line 78 def push(element) # Insert the item at the end of the heap: @contents.push(element) # Bubble it up into position: bubble_up(@contents.size - 1) # validate! return self end |
#size ⇒ Object
Returns the number of elements in the heap
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# File 'lib/timers/priority_heap.rb', line 43 def size @contents.size end |