The heapqueue module implements a binary heap data structure that can be used as a priority queue. They are represented as arrays for which a[k] <= a[2*k+1] and a[k] <= a[2*k+2] for all indices k (counting elements from 0). The interesting property of a heap is that a[0] is always its smallest element.
Basic usage
Example:
import std/heapqueue var heap = [8, 2].toHeapQueue heap.push(5) # the first element is the lowest element assert heap[0] == 2 # remove and return the lowest element assert heap.pop() == 2 # the lowest element remaining is 5 assert heap[0] == 5
Usage with custom objects
To use a HeapQueue with a custom object, the < operator must be implemented.
Example:
import std/heapqueue type Job = object priority: int proc `<`(a, b: Job): bool = a.priority < b.priority var jobs = initHeapQueue[Job]() jobs.push(Job(priority: 1)) jobs.push(Job(priority: 2)) assert jobs[0].priority == 1
Procs
proc `$`[T](heap: HeapQueue[T]): string
-
Turns a heap into its string representation.
Example:
let heap = [1, 2].toHeapQueue assert $heap == "[1, 2]"
Source Edit proc `[]`[T](heap: HeapQueue[T]; i: Natural): lent T {.inline.}
- Accesses the i-th element of heap. Source Edit
proc clear[T](heap: var HeapQueue[T])
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Removes all elements from heap, making it empty.
Example:
var heap = [9, 5, 8].toHeapQueue heap.clear() assert heap.len == 0
Source Edit proc del[T](heap: var HeapQueue[T]; index: Natural)
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Removes the element at index from heap, maintaining the heap invariant.
Example:
var heap = [9, 5, 8].toHeapQueue heap.del(1) assert heap[0] == 5 assert heap[1] == 8
Source Edit proc find[T](heap: HeapQueue[T]; x: T): int
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Linear scan to find the index of the item x or -1 if not found.
Example:
let heap = [9, 5, 8].toHeapQueue assert heap.find(5) == 0 assert heap.find(9) == 1 assert heap.find(777) == -1
Source Edit proc initHeapQueue[T](): HeapQueue[T]
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Creates a new empty heap.
Heaps are initialized by default, so it is not necessary to call this function explicitly.
See also:
Source Edit proc len[T](heap: HeapQueue[T]): int {.inline.}
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Returns the number of elements of heap.
Example:
let heap = [9, 5, 8].toHeapQueue assert heap.len == 3
Source Edit proc pop[T](heap: var HeapQueue[T]): T
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Pops and returns the smallest item from heap, maintaining the heap invariant.
Example:
var heap = [9, 5, 8].toHeapQueue assert heap.pop() == 5
Source Edit proc push[T](heap: var HeapQueue[T]; item: sink T)
- Pushes item onto heap, maintaining the heap invariant. Source Edit
proc pushpop[T](heap: var HeapQueue[T]; item: sink T): T
-
Fast version of a push() followed by a pop().
See also:
Example:
var heap = [5, 12].toHeapQueue assert heap.pushpop(6) == 5 assert heap.len == 2 assert heap[0] == 6 assert heap.pushpop(4) == 4
Source Edit proc replace[T](heap: var HeapQueue[T]; item: sink T): T
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Pops and returns 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.
See also:
Example:
var heap = [5, 12].toHeapQueue assert heap.replace(6) == 5 assert heap.len == 2 assert heap[0] == 6 assert heap.replace(4) == 6
Source Edit proc toHeapQueue[T](x: openArray[T]): HeapQueue[T]
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Creates a new HeapQueue that contains the elements of x.
See also:
Example:
var heap = [9, 5, 8].toHeapQueue assert heap.pop() == 5 assert heap[0] == 8
Source Edit