isTreeBalanced

    public boolean isTreeBalanced(Node root) {
        return (maxDepth(root) - minDepth(root)) <= 1;
    }

    public int maxDepth(Node root) {
        if (root == null) {
            return 0;
        }
        return 1 + Math.max(maxDepth(root.leftChild), maxDepth(root.rightChild));
    }

    public int minDepth(Node root) {
        if (root == null) {
            return 0;
        }
        return 1 + Math.min(minDepth(root.leftChild), minDepth(root.rightChild));
    }

    private class Node {
        Node leftChild;
        Node rightChild;
    }

Can't believe that's how easy it is... I thought too hard on how to calculate the depth of a tree node...