Flip Binary Tree To Match Preorder Traversal LeetCode solution in JavaScript

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var flipMatchVoyage = function (root, voyage) {
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  const output = [];
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  let idx = 0;
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  function run(node) {
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    if (!node) return true;
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    if (voyage[idx] !== node.val) return false;
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    idx++;
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    if (node.left && node.left.val !== voyage[idx]) {
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      output.push(node.val);
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      return run(node.right) && run(node.left);
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    }
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    return run(node.left) && run(node.right);
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  }
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  return run(root) ? output : [-1];
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};