added filter to leftistheap

containers.mllib

@@ -24,3 +24,4 @@ RAL
 MultiSet
 UnionFind
 SmallSet
+Leftistheap

leftistheap.ml

@@ -79,6 +79,16 @@ let insert heap x =
   let tree = merge_tree heap.leq (Node (1, x, Empty, Empty)) heap.tree in
   { heap with tree; }
 
+let filter heap p =
+  let rec filter tree p = match tree with
+  | Empty -> Empty
+  | Node (_, x, l, r) when p x ->
+    merge_tree heap.leq (Node (1, x, Empty, Empty))
+      (merge_tree heap.leq (filter l p) (filter r p))
+  | Node (_, _, l, r) -> merge_tree heap.leq (filter l p) (filter r p)
+  in
+  { heap with tree = filter heap.tree p; }
+
 let find_min heap =
   match heap.tree with
   | Empty -> raise Not_found

leftistheap.mli

@@ -46,6 +46,9 @@ val merge : 'a t -> 'a t -> 'a t
 val insert : 'a t -> 'a -> 'a t
   (** Insert a value in the heap *)
 
+val filter : 'a t -> ('a -> bool) -> 'a t
+  (** Filter values, only retaining the ones that satisfy the predicate *)
+
 val find_min : 'a t -> 'a
   (** Find minimal element, or raise Not_found *)