js-priority-queue/src/PriorityQueue/BinaryHeapStrategy.coffee

Priority queue data structures

module.exports = class BinaryHeapStrategy
  constructor: (options) ->
    @comparator = options?.comparator || (a, b) -> a - b
    @length = 0
    @data = (options.initialValues?.slice(0) || [])
    @_heapify()

  _heapify: ->
    if @data.length > 0
      for i in [ 1 ... @data.length ]
        @_bubbleUp(i)
    undefined

  queue: (value) ->
    @data.push(value)
    @_bubbleUp(@data.length - 1)
    undefined

  dequeue: ->
    ret = @data[0]
    last = @data.pop()
    if @data.length > 0
      @data[0] = last
      @_bubbleDown(0)
    ret

  peek: ->
    @data[0]

  clear: ->
    @length = 0
    @data.length = 0
    undefined

  _bubbleUp: (pos) ->
    while pos > 0
      parent = (pos - 1) >>> 1
      if @comparator(@data[pos], @data[parent]) < 0
        x = @data[parent]; @data[parent] = @data[pos]; @data[pos] = x
        pos = parent
      else
        break
    undefined

  _bubbleDown: (pos) ->
    last = @data.length - 1

    loop
      left = (pos << 1) + 1
      right = left + 1
      minIndex = pos
      if left <= last && @comparator(@data[left], @data[minIndex]) < 0
        minIndex = left
      if right <= last && @comparator(@data[right], @data[minIndex]) < 0
        minIndex = right

      if minIndex != pos
        x = @data[minIndex]; @data[minIndex] = @data[pos]; @data[pos] = x
        pos = minIndex
      else
        break
    undefined