题目: Given n, how many structurally unique BST's (binary search trees) that store values 1...n? For example,Given n = 3, there are a total of 5 unique BST's. 思路: 需要使用递推关系来解决. 对于n个结点,除去根节点,还剩余n-1个结点. 因此左右子树的结点数分配方式如下所示: (0,n-1), (1,n-2), (2, n-3), ....…