balanced binary tree

public boolean (TreeNode root) {
    return getHeight(root) != -1;
}

public int getHeight(TreeNode root) {
    if (root == null)
        return 0;
    int left = getHeight(root.left);
    if (left == -1)
        return -1;
    int right = getHeight(root.right);
    if (right == -1)
        return -1;
    if (Math.abs(right - left) > 1)
        return -1;
    return Math.max(left, right) + 1;
}