[CCHeap] add delete_once

src/core/CCHeap.ml

@@ -118,6 +118,11 @@ module type S = sig
   (** Same as {!take}, but can fail.
       @raise Empty if the heap is empty *)
 
+  val delete_once : (elt -> elt -> bool) -> elt -> t -> t
+  (** Delete one occurence of a value if it exist in the heap.
+      [delete_once eq x h], use [eq] to find one [x] in [h] and delete it.
+      If [h] do not contain [x] then it return [h]. *)
+
   val delete_all : (elt -> elt -> bool) -> elt -> t -> t
   (** Delete all occurrences of a value in the heap.
       [delete_all eq x h], use [eq] to find all [x] in [h] and delete them.
@@ -250,6 +255,26 @@ module Make(E : PARTIAL_ORD) : S with type elt = E.t = struct
     | E -> raise Empty
     | N (_, x, l, r) -> merge l r, x
 
+  let delete_once eq x h =
+    let rec aux = function
+      | E -> false, E
+      | N(_, y, l, r) as h -> begin
+        if eq x y then true, merge l r
+        else begin
+          if E.leq y x
+          then begin
+            let found_left, l1 = aux l in
+            let found, r1 = if found_left then true, r else aux r in
+            if found
+            then true, _make_node y l1 r1
+            else false, h
+          end
+          else false, h
+        end
+      end
+    in
+    snd (aux h)
+
   let rec delete_all eq x = function
     | E -> E
     | N (_, y, l, r) as h ->

src/core/CCHeap.mli

@@ -55,6 +55,12 @@ module type S = sig
   (** Same as {!take}, but can fail.
       @raise Empty if the heap is empty *)
 
+  val delete_once : (elt -> elt -> bool) -> elt -> t -> t
+  (** Delete one occurence of a value if it exist in the heap.
+      [delete_once eq x h], use [eq] to find one [x] in [h] and delete it.
+      If [h] do not contain [x] then it return [h].
+      @since NEXT_RELEASE *)
+
   val delete_all : (elt -> elt -> bool) -> elt -> t -> t
   (** Delete all occurrences of a value in the heap.
       [delete_all eq x h], use [eq] to find all [x] in [h] and delete them.