## 题目描述：

LeetCode 669. Trim a Binary Search Tree

Given a binary search tree and the lowest and highest boundaries as `L` and `R`, trim the tree so that all its elements lies in `[L, R]` (R >= L). You might need to change the root of the tree, so the result should return the new root of the trimmed binary search tree.

Example 1:

```Input:
1
/ \
0   2

L = 1
R = 2

Output:
1
\
2
```

Example 2:

```Input:
3
/ \
0   4
\
2
/
1

L = 1
R = 3

Output:
3
/
2
/
1
```

## Python代码：

``````# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
def trimBST(self, root, L, R):
"""
:type root: TreeNode
:type L: int
:type R: int
:rtype: TreeNode
"""
if not root: return None
if root.val < L:
return self.trimBST(root.right, L, R)
if root.val > R:
return self.trimBST(root.left, L, R)
root.left = self.trimBST(root.left, L, R)
root.right = self.trimBST(root.right, L, R)
return root
``````

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1. 书影网友 发布于 2017年9月4日 00:28 #

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