[CareerCup 4.1] Check whether a tree is balanced 書上答案似乎有錯誤

这么看确实有问题，应该递归的确认每个node的left-subtree和right-subtree的差，就想楼主写的那样....楼主太细心了！

The way to solve this problem is to start by writing a specification for the function you are trying to write.

Specification: A well-formed binary tree is said to be "height-balanced" if (1) it is empty, or (2) its left and right children are height-balanced and the height of the left tree is within 1 of the height of the right tree.

Now that you have the specification, the code is trivial to write. Just follow the specification:

IsHeightBalanced(tree)
    return (tree is empty) or
           (IsHeightBalanced(tree.left) and
            IsHeightBalanced(tree.right) and
            abs(Height(tree.left) - Height(tree.right)) <= 1)