Lua priority queue

Lua implementation of priority queue data structure using indirect binary heap( which are basically binary heaps with efficient search). Indirect heaps offer efficient removal and updating priority operations. This implementation is based on binaryheap libary with some changed design.

PriorityQueue.new( [array/ordering] )

Create new priority queue. You can pass array to initialize queue with O(n) complexity (implemented with batchenq, see below). First argument also could be an ordering function defining higher priority or you can simply pass "min" for min-heap( default behavior ) or "max" for max-heap (also array can contain higherpriority field).

Min heap:

local q = PriorityQueue.new()
local q = PriorityQueue.new('min') 

Max heap using function notation:

local q = PriorityQueue( 'max' )

Array initialization:

local security = PriorityQueue{ 
	'high', 1, 
	'low', 10, 
	'moderate', 5, 
	'moderate-', 7, 
	'moderate+', 3,
}

Array initialization with max-heap ordering:

local security = PriorityQueue{
	higherpriority = 'max',
	'high', 10, 
	'low', 1, 
	'moderate', 5, 
	'moderate-', 3, 
	'moderate+', 7,
}

Custom comparator:

local security = PriorityQueue{
	higherpriority = function(a,b)
		return a.level > b.level
	end,
	'high', {level = 10}, 
	'low', {level = 1}, 
	'moderate', {level = 5}, 
	'moderate-', {level = 3}, 
	'moderate+', {level = 7},
}

enqueue( item, priority )

Enqueue the item with the priority to the heap. The priority must be comparable if you use builtin comparators, i.e. it must be either number or string or a table with metatable with __lt metamethod defined. Otherwise you have to define custom comparator. Time complexity is O(logn).

dequeue()

Dequeue from the heap. Returns item and associated priority. If the heap is empty then an error will raise. Returns an item with highest priority. Time complexity is O(logn).

peek()

Returns the item with minimal priority and priority itself for BinaryMinHeap(maximal for BinaryMaxHeap) or nil if the heap is empty.

len()

Returns items count. Also you can use # operator for the same effect.

empty()

Returns true if the heap has no items and false otherwise.

batchenq( iparray )

Efficiently enqueues list of item-priority pairs into the heap. Note that this is efficient only when the amount of inserting elements greater or equal than the current length. Time complexity of this operation is O(n)(sequential approach is O(nlogn)).

contains( item )

Checking that heap contains the item. This operation is O(1).

remove( item )

Removes the item from the heap. Returns true if item was in the heap and false otherwise. This operation is O(logn).

update( item, priority )

Changes item priority. Returns true if item was in the queue (even if priority not changed) and false otherwise. This operation is O(logn), internally it's just remove followed by enqueue.