From 2b881acc2825dca8b2a8c0c2de70b6927f7a83ce Mon Sep 17 00:00:00 2001
From: Lars Mueller <appgurulars@gmx.de>
Date: Sat, 16 Jan 2021 17:17:29 +0100
Subject: [PATCH] Add min-heap

---
 heap.lua | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
 init.lua |  3 ++-
 test.lua | 15 +++++++++++++++
 3 files changed, 67 insertions(+), 1 deletion(-)
 create mode 100644 heap.lua

diff --git a/heap.lua b/heap.lua
new file mode 100644
index 0000000..5475541
--- /dev/null
+++ b/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
\ No newline at end of file
diff --git a/init.lua b/init.lua
index 10276e6..7210a8e 100644
--- a/init.lua
+++ b/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
diff --git a/test.lua b/test.lua
index 89e656a..3cf6e2c 100644
--- a/test.lua
+++ b/test.lua
@@ -54,4 +54,19 @@ if tests.liquid_raycast then
             end
         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
\ No newline at end of file