Average of Levels in Binary Tree LeetCode solution in Java

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class Solution {
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  public List<Double> averageOfLevels(TreeNode root) {
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    Queue<TreeNode> q = new LinkedList<>(List.of(root));
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    List<Double> ans = new ArrayList<>();
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    while (q.size() > 0) {
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      double qlen = q.size(), row = 0;
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      for (int i = 0; i < qlen; i++) {
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        TreeNode curr = q.poll();
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        row += curr.val;
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        if (curr.left != null) q.offer(curr.left);
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        if (curr.right != null) q.offer(curr.right);
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      }
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      ans.add(row / qlen);
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    }
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    return ans;
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  }
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}