Unique Subsets

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Unique Subsets

Given a list of numbers that may has duplicate numbers, return all possible subsets.

Example

If S = [1,2,2], a solution is:

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

Solution

    public ArrayList<ArrayList<Integer>> subsetsWithDup(ArrayList<Integer> S) {        ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();        if (S == null || S.size() == 0) {            return result;        }        Collections.sort(S);        ArrayList<Integer> path = new ArrayList<Integer>();        dfs(result, path, S, 0);        return result;    }    private void dfs(ArrayList<ArrayList<Integer>> result, ArrayList<Integer> path,         ArrayList<Integer> S, int pos){        result.add(new ArrayList<Integer>(path));        for (int i = pos; i < S.size(); i++) {            if (i > pos && S.get(i) == S.get(i - 1)) {                continue;            }            path.add(S.get(i));            dfs(result, path, S, i + 1);            path.remove(path.size() - 1);        }    }

思路：

duplication发生在当取完一种，后面是重复数字，不能再取。横向比较

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