Subsets II

https://oj.leetcode.com/problems/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],
  []
]

public List<List<Integer>> subsetsWithDup(int[] num)

哎，这题和Subset http://blog.youkuaiyun.com/chaochen1407/article/details/43369783 的区别就和 Combination Sum 跟 Combination Sum II 的区别是一样一样的。具体我就不再阐述了。大家就根据那两篇文章看吧。大致上Subset里面我也略有提到过。

    public List<List<Integer>> subsetsWithDup(int[] num) {
        List<List<Integer>> res = new LinkedList<List<Integer>>();
        Integer[] buf = new Integer[num.length];
        Arrays.sort(num);
        helper(res, 0, 0, buf, num);
        return res;
    }
    
    public void helper(List<List<Integer>> res, int curpos, int curlevel, Integer[] buf, int[] num){
        Integer[] cur_res = new Integer[curpos];
        System.arraycopy(buf, 0, cur_res, 0, curpos);
        res.add(Arrays.asList(cur_res));
        if(curlevel < num.length){
            for(int i = curlevel; i < num.length; i++){
                if(i != curlevel && num[i] == num[i - 1])//这个条件去掉了就是Subsets了。
                    continue;
                buf[curpos] = num[i];
                helper(res, curpos + 1, i + 1, buf, num);
            }
        }
    }