Is Balanced Binary Tree

public boolean isBalanced(TreeNode root) {
    return height(root) >= 0;
}

int height(TreeNode root) {
    if (root == null)
        return 0;
    int l, r;

    l = height(root.left);
    if (l == -1)
        return -1;
    r = height(root.right);
    if (r == -1)
        return -1;
    if (Math.abs(l-r) > 1) {
        return -1;
    } else {
        return Math.max(l, r) + 1;
    }
}