【leetcode刷題筆記】Subsets

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

Note:

• Elements in a subset must be 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],  [1,2,3],  [1,3],  [2,3],  [1,2],  []]

題解：實現一個遞迴的函數產生長度為level的所有子集放入結果中，然後迴圈的置這個level為0~S.length，即可產生所有的子集。

代碼如下：

 1 public class Solution { 2     public void subsetsDfs(int[] s,int level,int pos,ArrayList<Integer> result,List<List<Integer>> answer){ 3         if(result.size() == level){ 4             answer.add(new ArrayList<Integer>(result)); 5             return; 6         } 7         for(int i = pos;i < s.length;i++){ 8             result.add(s[i]); 9             subsetsDfs(s, level, i+1, result, answer);10             result.remove(result.size()-1);11         }12     }13     public List<List<Integer>> subsets(int[] S) {14         Arrays.sort(S);15         List<List<Integer>> answer = new ArrayList<List<Integer>>();16         ArrayList<Integer> result = new ArrayList<Integer>();17         18         for(int i = 0;i <= S.length;i++)19             subsetsDfs(S, i, 0, result, answer);20         return answer;21     }22 }