Add min-heap

heap.lua

@@ -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

init.lua

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

test.lua

@@ -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