public boolean isBalanced(TreeNode root) {

if (root == null) {

return true;

}

return (Math.abs(height(root.left) - height(root.right)) <= 1) && isBalanced(root.left) && isBalanced(root.right);

}

public int height(TreeNode root) {

if (root == null) {

return 0;

}

return Math.max(height(root.left), height(root.right)) + 1;

}