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class Solution {
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 public:
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  void fun(vector<int> &nums, vector<vector<int>> &ans, int i) {
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    if (i == nums.size()) {
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      ans.push_back(nums);
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      return;
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    }
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    int freq[21] = {0};
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    for (int j = i; j < nums.size(); j++) {
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      if (freq[nums[j] + 10] == 0) {
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        swap(nums[i], nums[j]);
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        fun(nums, ans, i + 1);
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        swap(nums[i], nums[j]);
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      }
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      freq[nums[j] + 10]++;
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    }
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  }
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  vector<vector<int>> permuteUnique(vector<int> &nums) {
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    vector<vector<int>> ans;
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    fun(nums, ans, 0);
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    return ans;
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  }
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};