【Leetcode】【python】Unique Binary Search Trees II

题目大意

解题思路

代码

class Solution(object):
def generateTrees(self, n):
if n == 0:
return []
return self.helper(1, n)

def helper(self, start, end):
result = []
if start > end:
result.append(None)
return result

for i in range(start, end + 1):
# generate left and right sub tree
leftTree = self.helper(start, i - 1)
rightTree = self.helper(i + 1, end)
# link left and right sub tree to root(i)
for j in range(len(leftTree)):
for k in range(len(rightTree)):
root = TreeNode(i)
root.left = leftTree[j]
root.right = rightTree[k]
result.append(root)

return result

总结