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Classic CLRS Huffman code example. ADT:
type tree = Leaf of int * char | Node of int * tree * tree
Build by repeatedly merging two lightest trees (sorted-list pq):
let rec build_tree lst = match lst with
| [t] -> t
| a :: b :: rest ->
let merged = Node (weight a + weight b, a, b) in
build_tree (insert merged rest)
weighted path length (= total Huffman bits):
leaves {(5,a) (9,b) (12,c) (13,d) (16,e) (45,f)} -> 224
Tests sum-typed ADT with mixed arities, `function` keyword
pattern matching, recursive sorted insert, depth-counting recursion.
150 baseline programs total.
39 lines
751 B
OCaml
39 lines
751 B
OCaml
type tree = Leaf of int * char | Node of int * tree * tree
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let weight = function
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| Leaf (w, _) -> w
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| Node (w, _, _) -> w
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let rec insert t lst =
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match lst with
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| [] -> [t]
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| h :: rest ->
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if weight t <= weight h then t :: lst
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else h :: insert t rest
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let rec build_tree lst =
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match lst with
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| [] -> failwith "empty"
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| [t] -> t
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| a :: b :: rest ->
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let merged = Node (weight a + weight b, a, b) in
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build_tree (insert merged rest)
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let rec depth d t =
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match t with
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| Leaf (w, _) -> w * d
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| Node (_, l, r) -> depth (d + 1) l + depth (d + 1) r
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;;
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let initial = [
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Leaf (5, 'a');
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Leaf (9, 'b');
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Leaf (12, 'c');
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Leaf (13, 'd');
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Leaf (16, 'e');
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Leaf (45, 'f')
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] in
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let t = build_tree initial in
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depth 0 t
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