Order two numerical lists

Order two numerical lists is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

Write function that orders two lists or arrays filled with numbers. The function should accept two lists as arguments and return true if the first list should be ordered before the second, and false otherwise.

The order is determined by lexicographic order: Comparing the first element of each list. If the first elements are equal, then the second elements should be compared, and so on, until one of the list has no more elements. If the first list runs out of elements the result is true. false otherwise.

Common Lisp

<lang Lisp>(defun list< (a b)

 (cond ((not a) t)
       ((not b) nil)
       ((= (first a) (first b))
        (list< (rest a) (rest b)))
       (t (< (first a) (first b)))))</lang>

Go

For numbers in the range 0 to 255: <lang go>func OrderTwoNumericalLists(a, b []byte) bool {

   return string(a) < string(b)

}</lang>

Java

Works with: Java version 1.5+

Translation of: Common Lisp

There are a few methods here. The method named "ordered" which works on arrays is a translation of Common Lisp. The other two are loose translations of Tcl (some tweaks were needed to get the length checks to work out) and are probably better options. <lang java5>import java.util.Arrays; import java.util.List;

public class ListOrder{ public static boolean ordered(double[] first, double[] second){ if(first.length == 0) return true; if(second.length == 0) return false; if(first[0] == second[0]) return ordered(Arrays.copyOfRange(first, 1, first.length), Arrays.copyOfRange(second, 1, second.length)); return first[0] < second[0]; }

public static boolean ordered(List<Double> first, List<Double> second){ int i = 0; for(; i < first.size() && i < second.size();i++){ if(first.get(i) == second.get(i)) continue; if(first.get(i) < second.get(i)) return true; return false; } return i == first.size(); }

public static boolean ordered2(double[] first, double[] second){ int i = 0; for(; i < first.length && i < second.length;i++){ if(first[i] == second[i]) continue; if(first[i] < second[i]) return true; return false; } return i == first.length; } }</lang>

OCaml

The function that achieves the task:

<lang ocaml>let rec ordered_lists = function

 | x1::tl1, x2::tl2 ->
     (match compare x1 x2 with
     | 0 -> ordered_lists (tl1, tl2)
     | 1 -> false
     | _ -> true)
 | [], _ -> true
 | _ -> false</lang>

Here is a small script to test this function:

<lang ocaml>(* copy-paste the code of ordered_lists here *)

let make_num_list p n =

 let rec aux acc =
   if Random.int p = 0 then acc
   else aux (Random.int n :: acc)
 in
 aux []

let print_num_list lst =

 List.iter (Printf.printf " %d") lst;
 print_newline()

let () =

 Random.self_init();
 let lst1 = make_num_list 8 5 in
 let lst2 = make_num_list 8 5 in
 print_num_list lst1;
 print_num_list lst2;
 Printf.printf "ordered: %B\n" (ordered_lists (lst1, lst2))</lang>

Sample execution:

$ ocaml ordered_lists.ml
 1 2 1 3 2
 1 2 0 4 4 0 0 0
ordered: false

Also notice that the function ordered_lists will work with anything the function Pervasives.compare is able to compare (most OCaml types and structures made from the base types). In the prototype of this function below 'a list means a list of anything:

<lang ocaml>val ordered_lists : 'a list * 'a list -> bool</lang>

Pike

<lang Pike>int(0..1) order_array(array a, array b) {

 if (!sizeof(a)) return true;
 if (!sizeof(b)) return false;
 if (a[0] == b[0])
   return order_array(a[1..], b[1..]);
 return a[0] < b[0];

}</lang>

Tcl

<lang tcl>proc numlist< {A B} {

   foreach a $A b $B {
       if {$a<$b} {
           return 1
       } elseif {$a>$b} {
           return 0
       }
   }
   return 0

}</lang>