Binary Tree Coloring Game LeetCode solution in JavaScript

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var left, right, val;
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var btreeGameWinningMove = function (root, n, x) {
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  function count(node) {
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    if (node == null) return 0;
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    var l = count(node.left);
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    var r = count(node.right);
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    if (node.val == val) {
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      left = l;
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      right = r;
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    }
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    return l + r + 1;
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  }
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  val = x;
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  count(root);
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  return Math.max(n - left - right - 1, Math.max(left, right)) > n / 2;
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};