local heap = require'heap'
Priority queues implemented as binary heaps. A binary heap is a binary tree that maintains the lowest (or highest) value at the root. The tree is laid as an implicit data structure over an array. Pushing and popping values from the heap is O(log(n)) and doesn’t use additional memory.
API
heap.heap(...) > push, pop 
create a heap API from a stack API 
heap.cdataheap(h) > h 
create a fixedcapacity cdatabased heap 
heap.valueheap([h]) > h 
create a heap for Lua values 
h:push(val) > index 
push a value 
h:pop([index][, dst]) > val 
pop value (root value at default index 1) 
h:replace(index, val) 
replace value at index 
h:peek([index][, dst]) > val 
get value without popping it 
h:length() > n 
number of elements in heap 
API Notes:
 a cdata heap can hold size1 elements (element 0 is used for swapping).
 trying to push nil into a value heap raises an error.
 values that compare equally are popped in random order.
heap.heap(push, pop, swap, len, cmp) > push, pop, rebalance
Create a heap API:
push(...) > i drop a value into the heap and return its index
pop(i) remove the value at index i (root is at index 1)
rebalance(i) rebalance the heap after the value at i has been changed
from a stack API:
push(...) add a value to the top of the stack
pop() remove the value at the top of the stack
swap(i, j) swap two values (indices start at 1)
len() > n number of elements in stack
cmp(i, j) > bool compare elements
The heap can be a minheap or maxheap depending on the comparison function. If cmp(i, j) returns a[i] < a[j] then it’s a minheap. Stack indices are assumed to be consecutive.
heap.cdataheap(h) > h
Create a cdata heap over table h
which must contain:
size
: heap capacity (required).
ctype
: element type (required).
data
, length
: a preallocated heap (optional).
cmp
: a comparison function (optional).
Example:
local h = heap.cdataheap{
size = 100,
ctype = [[
struct {
int priority;
int order;
}
]],
cmp = function(a, b)
if a.priority == b.priority then
return a.order > b.order
end
return a.priority < b.priority
end}
h:push{priority = 20, order = 1}
h:push{priority = 10, order = 2}
h:push{priority = 10, order = 3}
h:push{priority = 20, order = 4}
assert(h:pop().order == 3)
assert(h:pop().order == 2)
assert(h:pop().order == 4)
assert(h:pop().order == 1)
Note: the order
field in this example is used to stabilize the order in which elements with the same priority are popped.
heap.valueheap([h]) > h
Create a value heap from table h
, which can contain:
cmp
: a comparison function (optional).
 a preallocated heap in the array part of the table (optional).
Example:
local h = heap.valueheap{cmp = function(a, b)
return a.priority < b.priority
end}
h:push{priority = 20, etc = 'bar'}
h:push{priority = 10, etc = 'foo'}
assert(h:pop().priority == 10)
assert(h:pop().priority == 20)
TODO
 heapifying the initial array
 merge(h), meld(h)
Last updated:
2 years ago

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