Set的实现是通过２叉排序树来实现，就是将所有的元素用一个树来存储，根元素大于左子树的元素，小于右子树的元素，所有的操作都是基于这个树，通过判断元素的大小来选择对左子树操作还是右子树操作，这样操作数量和树的层数成正比-Set by the realization of two binary sort tree to achieve, that is, all the elements to store a tree, the root element is greater than the left subtree of the element, is less than the right subtree of the element, all operations are based on the tree, adopted to determine the size of elements to choose to operate on the left or right subtree subtree operation, the number of such operations and the rise in direct proportion to the tree