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var recoverTree = function (root) {
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  const arr = [];
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  const traverse = (r = root) => {
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    if (!r) return;
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    traverse(r.left);
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    arr.push(r.val);
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    traverse(r.right);
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  };
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  traverse();
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  arr.sort((a, b) => a - b);
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  let k = 0;
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  const recover = (r = root) => {
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    if (!r) return null;
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    recover(r.left);
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    r.val = arr[k++];
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    recover(r.right);
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  };
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  recover();
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  return root;
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};