Q: Given a set of distinct integers, nums, return all possible subsets.

Note: Elements in a subset must be in non-descending order;  The solution set must not contain duplicate subsets.

A: recursion problem 

 

Java version 1:

import java.util.Arrays;public class Solution {    public List
     
      
       > subsets(int[] nums) {        List
       
        
         > ans = new ArrayList
         
          
           >(); if (nums == null) return ans; Arrays.sort(nums); List
           
             ele = new ArrayList
            
             (); addElement(ans, ele, nums, 0, nums.length-1); return ans; } public void addElement(List
             
              
               > ans, List
               
                 ele, int[] nums, int start, int end){ if (start > end){ List
                
                  tmp = new ArrayList
                 
                  (ele); ans.add(tmp); return; } for(int i = start; i <= end; i++){ ele.add(nums[i]); addElement(ans, ele, nums, i+1, end); ele.remove(ele.size()-1); } List
                  
                    tmp = new ArrayList
                   
                    (ele); ans.add(tmp); return; }}