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class Solution {
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 public:
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  int n;
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  vector<int> recoverArray(vector<int> &nums) {
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    sort(nums.begin(), nums.end());
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    int n2 = nums.size();
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    n = n2 / 2;
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    int a = nums[0];
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    vector<int> v1, v2, ans;
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    v1.reserve(n);
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    v2.reserve(n);
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    for (int i = 1; i < n2; i++) {
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      int k = nums[i] - a;
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      if (k % 2 == 1 || k == 0 || nums[i] == nums[i - 1]) continue;
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      v1.clear();
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      v2.clear();
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      v1.push_back(a);
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      int x = 0;
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      for (int j = 1; j < n2; j++) {
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        if (x < v1.size() && (nums[j] == v1[x] + k)) {
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          v2.push_back(nums[j]);
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          x++;
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        } else
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          v1.push_back(nums[j]);
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        if (v1.size() > n || v2.size() > n) break;
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      }
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      if (v1.size() != n || v2.size() != n) continue;
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      for (int i = 0; i < n; i++) ans.push_back((v1[i] + v2[i]) / 2);
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      return ans;
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    }
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    return ans;
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  }
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};