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    <p>You want a powerset. Here are all the questions on StackOverflow that mention <a href="https://stackoverflow.com/search?q=%22powerset%22">powersets</a> or <a href="https://stackoverflow.com/search?q=%22power+set%22">power sets</a>.</p> <p>Here is a basic implementation in python:</p> <pre><code>def powerset(s): n = len(s) masks = [1&lt;&lt;j for j in xrange(n)] for i in xrange(2**n): yield [s[j] for j in range(n) if (masks[j] &amp; i)] if __name__ == '__main__': for elem in powerset([1,2,3,4,5]): print elem </code></pre> <p>And here is its output:</p> <pre><code>[] [1] [2] [1, 2] [3] [1, 3] [2, 3] [1, 2, 3] [4] [1, 4] [2, 4] [1, 2, 4] [3, 4] [1, 3, 4] [2, 3, 4] [1, 2, 3, 4] [5] [1, 5] [2, 5] [1, 2, 5] [3, 5] [1, 3, 5] [2, 3, 5] [1, 2, 3, 5] [4, 5] [1, 4, 5] [2, 4, 5] [1, 2, 4, 5] [3, 4, 5] [1, 3, 4, 5] [2, 3, 4, 5] [1, 2, 3, 4, 5] </code></pre> <p>Notice that its first result is the empty set. Change the iteration from this <code>for i in xrange(2**n):</code> to this <code>for i in xrange(1, 2**n):</code> if you want to skip an empty set.</p> <p>Here is the code adapted to produce string output:</p> <pre><code>def powerset(s): n = len(s) masks = [1&lt;&lt;j for j in xrange(n)] for i in xrange(2**n): yield "".join([str(s[j]) for j in range(n) if (masks[j] &amp; i)]) </code></pre> <hr> <p>Edit 2009-10-24</p> <p>Okay, I see you are partial to an implementation in Java. I don't know Java, so I'll meet you halfway and give you code in C#:</p> <pre><code> static public IEnumerable&lt;IList&lt;T&gt;&gt; powerset&lt;T&gt;(IList&lt;T&gt; s) { int n = s.Count; int[] masks = new int[n]; for (int i = 0; i &lt; n; i++) masks[i] = (1 &lt;&lt; i); for (int i = 0; i &lt; (1 &lt;&lt; n); i++) { List&lt;T&gt; newList = new List&lt;T&gt;(n); for (int j = 0; j &lt; n; j++) if ((masks[j] &amp; i) != 0) newList.Add(s[j]); yield return newList; } } </code></pre>
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    1. POHow to obtain all subsequence combinations of a String (in Java, or C++ etc)
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    1. POHow to obtain all subsequence combinations of a String (in Java, or C++ etc)
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    1. COSomeone downvoted this -- why? Because I returned to this and added code in C# (and not Java!) to do what the OP asked? Sheesh. Glad I went the extra mile.
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    2. COOrder could be important in the poster's sequence, and it might be that elements occur more than once. Thus, the power set may not really help that much.
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    3. COSolved! Thanks.
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      1. USAhmet Alp Balkan - Google
 

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