tasks a-s

Task/Permutations/OCaml/permutations-1.ocaml

@@ -0,0 +1,45 @@
+(* Iterative, though loops are implemented as auxiliary recursive functions.
+   Translation of Ada version. *)
+let next_perm p =
+	let n = Array.length p in
+	let i = let rec aux i =
+		if (i < 0) || (p.(i) < p.(i+1)) then i
+		else aux (i - 1) in aux (n - 2) in
+	let rec aux j k = if j < k then
+		let t = p.(j) in
+			p.(j) <- p.(k);
+			p.(k) <- t;
+			aux (j + 1) (k - 1)
+	else () in aux (i + 1) (n - 1);
+	if i < 0 then false else
+		let j = let rec aux j =
+			if p.(j) > p.(i) then j
+			else aux (j + 1) in aux (i + 1) in
+		let t = p.(i) in
+			p.(i) <- p.(j);
+			p.(j) <- t;
+			true;;
+
+let print_perm p =
+	let n = Array.length p in
+	for i = 0 to n - 2 do
+		print_int p.(i);
+		print_string " "
+	done;
+	print_int p.(n - 1);
+	print_newline ();;
+
+let print_all_perm n =
+	let p = Array.init n (function i -> i + 1) in
+	print_perm p;
+	while next_perm p do
+		print_perm p
+	done;;
+
+print_all_perm 3;;
+(* 1 2 3
+   1 3 2
+   2 1 3
+   2 3 1
+   3 1 2
+   3 2 1 *)

Task/Permutations/OCaml/permutations-2.ocaml

@@ -0,0 +1,15 @@
+let rec permutations l =
+   let n = List.length l in
+   if n = 1 then [l] else
+   let rec sub e = function
+      | [] -> failwith "sub"
+      | h :: t -> if h = e then t else h :: sub e t in
+   let rec aux k =
+      let e = List.nth l k in
+      let subperms = permutations (sub e l) in
+      let t = List.map (fun a -> e::a) subperms in
+      if k < n-1 then List.rev_append t (aux (k+1)) else t in
+   aux 0;;
+
+let print l = List.iter (Printf.printf " %d") l; print_newline() in
+List.iter print (permutations [1;2;3;4])

Task/Permutations/OCaml/permutations-3.ocaml

@@ -0,0 +1,17 @@
+let rec pr_perm k n l =
+   let a, b = let c = k/n in c, k-(n*c) in
+   let e = List.nth l b in
+   let rec sub e = function
+      | [] -> failwith "sub"
+      | h :: t -> if h = e then t else h :: sub e t in
+   (Printf.printf " %d" e; if n > 1 then pr_perm a (n-1) (sub e l))
+
+let show_perms l =
+   let n = List.length l in
+   let rec fact n = if n < 3 then n else n * fact (n-1) in
+   for i = 0 to (fact n)-1 do
+      pr_perm i n l;
+      print_newline()
+   done
+
+let () = show_perms [1;2;3;4]