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class Solution {
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  private static void solve(int[] nums, int i, List<Integer> temp, List<List<Integer>> subset) {
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    if (i == nums.length) {
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      subset.add(new ArrayList(temp));
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      return;
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    }
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    temp.add(nums[i]);
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    solve(nums, i + 1, temp, subset);
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    temp.remove(temp.size() - 1);
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    solve(nums, i + 1, temp, subset);
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  }
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  public List<List<Integer>> subsets(int[] nums) {
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    List<List<Integer>> subset = new ArrayList();
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    List<Integer> temp = new ArrayList<>();
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    if (nums.length == 0) return subset;
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    int startInd = 0;
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    solve(nums, startInd, temp, subset);
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    return subset;
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  }
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}