Source file fheap.ml

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
open! Core
module Array = Base.Array
module List = Base.List
module Option = Base.Option
module Sequence = Base.Sequence

module Node = struct
  type 'a t =
    { value : 'a
    ; children : 'a t list
    }
end

open Node

type 'a t =
  { compare : 'a -> 'a -> int
  ; length : int
  ; heap : 'a Node.t option
  }

let create ~compare = { compare; length = 0; heap = None }

let merge
      ~compare
      ({ value = e1; children = nl1 } as n1)
      ({ value = e2; children = nl2 } as n2)
  =
  if compare e1 e2 < 0
  then { value = e1; children = n2 :: nl1 }
  else { value = e2; children = n1 :: nl2 }
;;

let merge_pairs ~compare t =
  let rec loop acc t =
    match t with
    | [] -> acc
    | [ head ] -> head :: acc
    | head :: next1 :: next2 -> loop (merge ~compare head next1 :: acc) next2
  in
  match loop [] t with
  | [] -> None
  | [ h ] -> Some h
  | x :: xs -> Some (List.fold xs ~init:x ~f:(merge ~compare))
;;

let add { compare; length; heap } e =
  let new_node = { value = e; children = [] } in
  let heap =
    match heap with
    | None -> new_node
    | Some heap -> merge ~compare new_node heap
  in
  { compare; length = length + 1; heap = Some heap }
;;

let top_exn t =
  match t.heap with
  | None -> failwith "Fheap.top_exn called on an empty heap"
  | Some { value; _ } -> value
;;

let top t =
  try Some (top_exn t) with
  | _ -> None
;;

let pop_exn { compare; length; heap } =
  match heap with
  | None -> failwith "Heap.pop_exn called on an empty heap"
  | Some { value; children } ->
    let new_heap = merge_pairs ~compare children in
    let t' = { compare; length = length - 1; heap = new_heap } in
    value, t'
;;

let pop t =
  try Some (pop_exn t) with
  | _ -> None
;;

let pop_min = pop
let pop_min_exn = pop_exn

let remove_top t =
  try
    let _, t' = pop_exn t in
    Some t'
  with
  | _ -> None
;;

let pop_if t f =
  match top t with
  | None -> None
  | Some v -> if f v then pop t else None
;;

let fold t ~init ~f =
  let rec loop acc to_visit =
    match to_visit with
    | [] -> acc
    | { value; children } :: rest ->
      let acc = f acc value in
      let to_visit = List.unordered_append children rest in
      loop acc to_visit
  in
  match t.heap with
  | None -> init
  | Some node -> loop init [ node ]
;;

let length t = t.length

module C = Container.Make (struct
    type nonrec 'a t = 'a t

    let fold = fold
    let iter = `Define_using_fold
    let length = `Custom length
  end)

let is_empty t = Option.is_none t.heap
let iter = C.iter
let mem = C.mem
let min_elt = C.min_elt
let max_elt = C.max_elt
let find = C.find
let find_map = C.find_map
let for_all = C.for_all
let exists = C.exists
let sum = C.sum
let count = C.count
let to_list = C.to_list
let fold_result = C.fold_result
let fold_until = C.fold_until

(* We could avoid the intermediate list here, but it doesn't seem like a big deal. *)
let to_array = C.to_array

let of_fold c ~compare fold =
  let h = create ~compare in
  fold c ~init:h ~f:add
;;

let of_list l ~compare = of_fold l ~compare List.fold
let of_array arr ~compare = of_fold arr ~compare Array.fold
let sexp_of_t sexp_of_a t = List.sexp_of_t sexp_of_a (to_list t)
let to_sequence t = Sequence.unfold ~init:t ~f:pop