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Added heapqueue collection. Fixed timers in asyncdispatch.
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Yuriy Glukhov
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Apr 27, 2016
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##[ Heap queue algorithm (a.k.a. priority queue). Ported from Python heapq. | ||
Heaps are arrays for which a[k] <= a[2*k+1] and a[k] <= a[2*k+2] for | ||
all k, counting elements from 0. For the sake of comparison, | ||
non-existing elements are considered to be infinite. The interesting | ||
property of a heap is that a[0] is always its smallest element. | ||
]## | ||
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type HeapQueue*[T] = distinct seq[T] | ||
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proc newHeapQueue*[T](): HeapQueue[T] {.inline.} = HeapQueue[T](newSeq[T]()) | ||
proc newHeapQueue*[T](h: var HeapQueue[T]) {.inline.} = h = HeapQueue[T](newSeq[T]()) | ||
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proc len*[T](h: HeapQueue[T]): int {.inline.} = seq[T](h).len | ||
proc `[]`*[T](h: HeapQueue[T], i: int): T {.inline.} = seq[T](h)[i] | ||
proc `[]=`[T](h: var HeapQueue[T], i: int, v: T) {.inline.} = seq[T](h)[i] = v | ||
proc add[T](h: var HeapQueue[T], v: T) {.inline.} = seq[T](h).add(v) | ||
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proc heapCmp[T](x, y: T): bool {.inline.} = | ||
return (x < y) | ||
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# 'heap' is a heap at all indices >= startpos, except possibly for pos. pos | ||
# is the index of a leaf with a possibly out-of-order value. Restore the | ||
# heap invariant. | ||
proc siftdown[T](heap: var HeapQueue[T], startpos, p: int) = | ||
var pos = p | ||
var newitem = heap[pos] | ||
# Follow the path to the root, moving parents down until finding a place | ||
# newitem fits. | ||
while pos > startpos: | ||
let parentpos = (pos - 1) shr 1 | ||
let parent = heap[parentpos] | ||
if heapCmp(newitem, parent): | ||
heap[pos] = parent | ||
pos = parentpos | ||
else: | ||
break | ||
heap[pos] = newitem | ||
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proc siftup[T](heap: var HeapQueue[T], p: int) = | ||
let endpos = len(heap) | ||
var pos = p | ||
let startpos = pos | ||
let newitem = heap[pos] | ||
# Bubble up the smaller child until hitting a leaf. | ||
var childpos = 2*pos + 1 # leftmost child position | ||
while childpos < endpos: | ||
# Set childpos to index of smaller child. | ||
let rightpos = childpos + 1 | ||
if rightpos < endpos and not heapCmp(heap[childpos], heap[rightpos]): | ||
childpos = rightpos | ||
# Move the smaller child up. | ||
heap[pos] = heap[childpos] | ||
pos = childpos | ||
childpos = 2*pos + 1 | ||
# The leaf at pos is empty now. Put newitem there, and bubble it up | ||
# to its final resting place (by sifting its parents down). | ||
heap[pos] = newitem | ||
siftdown(heap, startpos, pos) | ||
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proc push*[T](heap: var HeapQueue[T], item: T) = | ||
## Push item onto heap, maintaining the heap invariant. | ||
(seq[T](heap)).add(item) | ||
siftdown(heap, 0, len(heap)-1) | ||
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proc pop*[T](heap: var HeapQueue[T]): T = | ||
## Pop the smallest item off the heap, maintaining the heap invariant. | ||
let lastelt = seq[T](heap).pop() | ||
if heap.len > 0: | ||
result = heap[0] | ||
heap[0] = lastelt | ||
siftup(heap, 0) | ||
else: | ||
result = lastelt | ||
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proc replace*[T](heap: var HeapQueue[T], item: T): T = | ||
## Pop and return the current smallest value, and add the new item. | ||
## This is more efficient than pop() followed by push(), and can be | ||
## more appropriate when using a fixed-size heap. Note that the value | ||
## returned may be larger than item! That constrains reasonable uses of | ||
## this routine unless written as part of a conditional replacement: | ||
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## if item > heap[0]: | ||
## item = replace(heap, item) | ||
result = heap[0] | ||
heap[0] = item | ||
siftup(heap, 0) | ||
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proc pushpop*[T](heap: var HeapQueue[T], item: T): T = | ||
## Fast version of a push followed by a pop. | ||
if heap.len > 0 and heapCmp(heap[0], item): | ||
swap(item, heap[0]) | ||
siftup(heap, 0) | ||
return item | ||
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when isMainModule: | ||
# Simple sanity test | ||
var heap = newHeapQueue[int]() | ||
let data = [1, 3, 5, 7, 9, 2, 4, 6, 8, 0] | ||
for item in data: | ||
push(heap, item) | ||
doAssert(heap[0] == 0) | ||
var sort = newSeq[int]() | ||
while heap.len > 0: | ||
sort.add(pop(heap)) | ||
doAssert(sort == @[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]) |