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class Solution {
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 public:
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  vector<int> sortArrayByParityII(vector<int> &nums) {
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    vector<int> ans(nums.size());
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    int even_idx = 0;
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    int odd_idx = 1;
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    for (int i = 0; i < nums.size(); i++) {
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      if ((nums[i] % 2) == 0) // the num is even
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      {
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        ans[even_idx] = nums[i];
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        even_idx += 2;
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      } else // the num is odd
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      {
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        ans[odd_idx] = nums[i];
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        odd_idx += 2;
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      }
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    }
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    return ans;
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  }
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};