843. Time Complexity: Repeated Tree Height

function height(root) {
  if (!root) return 0
  return 1 + Math.max(height(root.left), height(root.right))
}

function isBalanced(root) {
  if (!root) return true
  return Math.abs(height(root.left) - height(root.right)) <= 1 &&
    isBalanced(root.left) &&
    isBalanced(root.right)
}