The heapqueue module implements a heap data structure that can be used as a priority queue. 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. The interesting property of a heap is that a[0] is always its smallest element.
Basic usage
import heapqueue var heap = initHeapQueue[int]() heap.push(8) heap.push(2) 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 object
To use a HeapQueue with a custom object, the < operator must be implemented.
import 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 initHeapQueue[T](): HeapQueue[T]
-
Create a new empty heap.
See also:
Source Edit proc len[T](heap: HeapQueue[T]): int {...}{.inline.}
- Return the number of elements of heap. Source Edit
proc `[]`[T](heap: HeapQueue[T]; i: Natural): T {...}{.inline.}
- Access the i-th element of heap. Source Edit
proc push[T](heap: var HeapQueue[T]; item: T)
- Push item onto heap, maintaining the heap invariant. Source Edit
proc toHeapQueue[T](x: openArray[T]): HeapQueue[T]
-
Creates a new HeapQueue that contains the elements of x.
See also:
Example:
var heap = toHeapQueue([9, 5, 8]) assert heap.pop() == 5 assert heap[0] == 8
Source Edit proc pop[T](heap: var HeapQueue[T]): T
- Pop and return the smallest item from heap, maintaining the heap invariant. Source Edit
proc find[T](heap: HeapQueue[T]; x: T): int
- Linear scan to find index of item x or -1 if not found. Source Edit
proc del[T](heap: var HeapQueue[T]; index: Natural)
- Removes the element at index from heap, maintaining the heap invariant. Source Edit
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:
if item > heap[0]: item = replace(heap, item)
Source Edit proc pushpop[T](heap: var HeapQueue[T]; item: T): T
- Fast version of a push followed by a pop. Source Edit
proc clear[T](heap: var HeapQueue[T])
-
Remove all elements from heap, making it empty.
Example:
var heap = initHeapQueue[int]() heap.push(1) heap.clear() assert heap.len == 0
Source Edit proc `$`[T](heap: HeapQueue[T]): string
-
Turn a heap into its string representation.
Example:
var heap = initHeapQueue[int]() heap.push(1) heap.push(2) assert $heap == "[1, 2]"
Source Edit