https://leetcode.com/problems/subsets/

SubSets.java

//https://leetcode.com/problems/subsets/
//一种思路
public class Solution {
    /*
     * Given a set S of n distinct integers, there is a relation between Sn and Sn-1. The subset
     * of Sn is the union of subset of Sn-1 and each element in Sn-1 + one more element.
     * Therefore, a Java solution can be quickly formalized.
     */
     
    public static List<List<Integer>> ans = new ArrayList<List<Integer>>();
    public List<List<Integer>> subsets(int[] nums) {
        ans.clear();
        if(nums == null){
            return null;
        }
        
        Arrays.sort(nums);
        
        for(int i = 0;i<nums.length;i++){
            List<List<Integer>> tmp = new ArrayList<List<Integer>>();
            for(List<Integer> a : ans){
                tmp.add(new ArrayList(a));
            }
            for(List<Integer> t : tmp){
                t.add(nums[i]);
            }
            List<Integer> single = new ArrayList<Integer>();
            single.add(nums[i]);
            tmp.add(single);
            ans.addAll(tmp);
        }
        
        ans.add(new ArrayList<Integer>());
        
        return ans;
    }
}