added PriorityQueue

utils/PriorityQueue.lua

@@ -0,0 +1,74 @@
+local PriorityQueue = {}
+
+function PriorityQueue.new()
+    return {}
+end
+
+local function default_comp(a, b)
+    return a < b
+end
+
+local function HeapifyFromEndToStart(queue, comp)
+    comp = comp or default_comp
+    local pos = #queue
+    while pos > 1 do
+        local parent = bit32.rshift(pos, 1) -- integer division by 2
+        if comp(queue[pos], queue[parent]) then
+            queue[pos], queue[parent] = queue[parent], queue[pos]
+            pos = parent
+        else
+            break
+        end
+    end
+end
+
+local function HeapifyFromStartToEnd(queue, comp)
+    comp = comp or default_comp
+    local parent = 1
+    local smallest = 1
+    while true do
+        local child = parent * 2
+        if child > #queue then
+            break
+        end
+        if comp(queue[child], queue[parent]) then
+            smallest = child
+        end
+        child = child + 1
+        if child <= #queue and comp(queue[child], queue[smallest]) then
+            smallest = child
+        end
+
+        if parent ~= smallest then
+            queue[parent], queue[smallest] = queue[smallest], queue[parent]
+            parent = smallest
+        else
+            break
+        end
+    end
+end
+
+function PriorityQueue.size(queue)
+    return #queue
+end
+
+function PriorityQueue.push(queue, element, comp)
+    table.insert(queue, element)
+    HeapifyFromEndToStart(queue, comp)
+end
+
+function PriorityQueue.pop(queue, comp)
+    local element = queue[1]
+
+    queue[1] = queue[#queue]
+    queue[#queue] = nil
+    HeapifyFromStartToEnd(queue, comp)
+
+    return element
+end
+
+function PriorityQueue.peek(queue)
+    return queue[1]
+end
+
+return PriorityQueue