LeetCode Subsets II

Given a collection of integers that might contain duplicates, 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 = [1,2,2], a solution is:

[
  [2],
  [1],
  [1,2,2],
  [2,2],
  [1,2],
  []
]

每一次都在前一次的基础上添加新的数就行了。

public class Solution {
    public List<List<Integer>> subsetsWithDup(int[] num) {
        List<List<Integer>> result = new ArrayList<List<Integer>>();
        result.add(new ArrayList<Integer>());
        if (num.length == 0) {
            return result;
        }
        Arrays.sort(num);
        for (int i = 0; i < num.length; i++) {
            List<List<Integer>> current = new ArrayList<List<Integer>>(result);
            for (List<Integer> list : result) {
                List<Integer> newlist = new ArrayList<Integer>(list);
                newlist.add(num[i]);
                if (!current.contains(newlist)) {
                    current.add(newlist);
                }
            }
            result = current;
        }
        return result;
    }
}