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title :

Given a set of distinct integers, S, return all possible subsets.

Note:

• Elements in a subset must is in non-descending order.
• The solution set must not contain duplicate subsets.

For example,
If S = [1,2,3] , a solution is:

[  3],  [1], [2], [1,3], [+]  ,  [2,3], [up  ],  []]

 The following:
One idea is to apply the method of combination, in fact, combination that the problem is to ask for different n under the subset, here is actually asking for a set.
For example K=3,n=1, the method of combination the problem to obtain the set is [[1], [2], [3]];
    K=3, n=2, uses the method of combination that problem to obtain the set is [[1, 2], [1, 3], [2, 3]]
    K=3, n=3, using the method of combination that problem to find the set is [[[+]]
So the above 3 sets plus an empty set are not
[  3],  [1], [2], [1,3], [+]  ,  [2,3], [up  ],  []]
Do you?
Just add a loop to the outside of the combination.

The code is as follows:

1  Public Static voidDfsint[] S,intStartintLen, arraylist<integer> item,arraylist<arraylist<integer>>Res) {2         if(item.size () = =Len) {3Res.add (NewArraylist<integer>(item));4             return;5         }6          for(intI=start; i<s.length;i++){7 Item.add (S[i]);8DFS (S, i+1, Len, item, RES);9Item.remove (Item.size ()-1);Ten         } One  A     } -      -      Public Staticarraylist<arraylist<integer>> Subsets (int[] S) { thearraylist<arraylist<integer>> res =NewArraylist<arraylist<integer>> (); -arraylist<integer> item =NewArraylist<integer>(); -         if(s.length==0| | s==NULL) -             returnRes; +          - Arrays.sort (S); +          for(intlen = 1; Len<= s.length; len++) ADFS (s,0, len,item,res); at              -Res.add (NewArraylist<integer>()); -          -         returnRes; -}

reference:http://blog.csdn.net/worldwindjp/article/details/23300545

The bottom is another very refined algorithm.

1  Public Static voidDfsint[] S,intStart, arraylist<integer> item,arraylist<arraylist<integer>>Res) {2          for(intI=start; i<s.length;i++){3 Item.add (S[i]);4Res.add (NewArraylist<integer>(item));5DFS (s,i+1, item,res);6Item.remove (Item.size ()-1);7         }8 9     }Ten      One      Public Staticarraylist<arraylist<integer>> Subsets (int[] S) { Aarraylist<arraylist<integer>> res =NewArraylist<arraylist<integer>> (); -arraylist<integer> item =NewArraylist<integer>(); -         if(s.length==0| | s==NULL) the             returnRes; -          - Arrays.sort (S); -DFS (s,0, item,res); +Res.add (NewArraylist<integer>()); -          +         returnRes; A}

reference:http://blog.csdn.net/u011095253/article/details/9158397
Http://www.cnblogs.com/springfor/p/3879830.html

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