[leetcode tree]95. Unique Binary Search Trees II

Given an integer n, generate all structurally unique BST's (binary search trees) that store values 1...n.

For example,
Given n = 3, your program should return all 5 unique BST's shown below.

   1         3     3      2      1
    \       /     /      / \      \
     3     2     1      1   3      2
    /     /       \                 \
   2     1         2                 3

输入n,求出所有1-n组成的所有可能的树

 class Solution(object):
     def generateTrees(self, n):
         def node(v,l,r):
             n = TreeNode(v)
             n.left = l
             n.right = r
             return n
         def tree(first,last):
             return [node(v,l,r) for v in range(first,last+1)
                                 for l in tree(first,v-1)
                                 for r in tree(v+1,last)] or [None]
         return tree(1,n) if n else []