Add min-heap

This commit is contained in:
Lars Mueller 2021-01-16 17:17:29 +01:00
parent 61b48e09da
commit 2b881acc28
3 changed files with 67 additions and 1 deletions

50
heap.lua Normal file

@ -0,0 +1,50 @@
local metatable = {__index = getfenv(1)}
function default_less_than(a, b) return a < b end
--> empty min heap
function new(less_than)
return setmetatable({less_than = less_than or default_less_than}, metatable)
end
function push(self, value)
table.insert(self, value)
local function heapify(index)
if index == 1 then
return
end
local parent = math.floor(index / 2)
if self.less_than(self[index], self[parent]) then
self[parent], self[index] = self[index], self[parent]
heapify(parent)
end
end
heapify(#self)
end
function pop(self)
local value = self[1]
local last = #self
if last == 1 then
self[1] = nil
return value
end
self[1], self[last] = self[last], nil
last = last - 1
local function heapify(index)
local left_child = index * 2
if left_child > last then
return
end
local smallest_child = left_child + 1
if smallest_child > last or self.less_than(self[left_child], self[smallest_child]) then
smallest_child = left_child
end
if self.less_than(self[smallest_child], self[index]) then
self[index], self[smallest_child] = self[smallest_child], self[index]
heapify(smallest_child)
end
end
heapify(1)
return value
end

@ -68,7 +68,8 @@ for _, component in ipairs{
"text",
"vector",
"minetest",
"trie"
"trie",
"heap"
} do
modlib[component] = loadfile_exports(get_resource(component .. ".lua"))
end

@ -55,3 +55,18 @@ if tests.liquid_raycast then
end
end)
end
local n = 100
local list = {}
for index = 1, n do
list[index] = index
end
modlib.table.shuffle(list)
local heap = modlib.heap.new()
for index = 1, #list do
heap:push(list[index])
end
for index = 1, #list do
local popped = heap:pop()
assert(popped == index)
end