Non-continuous subsequences: Difference between revisions

=={{header|C sharp}}==

<lang csharp>using System;

using System.Collections.Generic;

using System.Linq;

class Program

{

public static void Main() {

var sequence = new[] { "A", "B", "C", "D" };

foreach (var subset in Subsets(sequence.Length).Where(s => !IsContinuous(s))) {

Console.WriteLine(string.Join(" ", subset.Select(i => sequence[i])));

}

}

static IEnumerable<List<int>> Subsets(int length) {

int[] values = Enumerable.Range(0, length).ToArray();

var stack = new Stack<int>(length);

for (int i = 0; stack.Count > 0 || i < length; ) {

if (i < length) {

stack.Push(i++);

yield return (from index in stack.Reverse() select values[index]).ToList();

} else {

i = stack.Pop() + 1;

if (stack.Count > 0) i = stack.Pop() + 1;

}

}

}

static bool IsContinuous(List<int> list) => list[list.Count - 1] - list[0] + 1 == list.Count;

}</lang>

{{out}}

<pre>

A B D

A C

A C D

A D

B D

</pre>

=={{header|Raku}}==

(formerly Perl 6)

{{works with|rakudo|2015-09-24}}

<lang perl6>sub non_continuous_subsequences ( *@list ) {

@list.combinations.grep: { 1 != all( .[ 0 ^.. .end] Z- .[0 ..^ .end] ) }

}

say non_continuous_subsequences( 1..3 )».gist;

say non_continuous_subsequences( 1..4 )».gist;

say non_continuous_subsequences( ^4 ).map: {[<a b c d>[.list]].gist};</lang>

{{out}}

<pre>((1 3))

((1 3) (1 4) (2 4) (1 2 4) (1 3 4))

([a c] [a d] [b d] [a b d] [a c d])</pre>