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
这道题描述的需求是：
给我们一个二叉排序树 最小数l 和最大数r
我们需要做的是对这棵树进行裁剪，让树里所有的节点值都满足在l和r之间
思想：
二叉排序树的特点是：对于任意一个节点，左子树任意节点数值都比跟节点小，右子树任意节点数值都比根大
所以考虑，对于任意一个节点，
如果值比l还小，那就应该抛弃这个根，去右子树寻找新的根
如果值比r还大，那就应该抛弃这个根，去左子树寻找新的根
这样的操作进行递归就可以了
我的python代码：
1 # Definition for a binary tree node.
2 class TreeNode:
3 def __init__(self, x):
4 self.val = x
5 self.left = None
6 self.right = None
7
8 class Solution:
9 def trimBST(self, root, L, R):
10 """
11 :type root: TreeNode
12 :type L: int
13 :type R: int
14 :rtype: TreeNode
15 """
16 if root is None:
17 return None
18 if root.val >R:
19 return self.trimBST(root.left ,L,R)
20 if root.val<L:
21 return self.trimBST(root.right, L, R)
22 root.left = self.trimBST(root.left,L,R)
23 root.right = self.trimBST(root.right,L,R)
24 return root
25
26
27
28 if __name__ == '__main__':
29 s = Solution()
30
31 root = TreeNode(1)
32 root.left = TreeNode(0)
33 root.right = TreeNode(2)
34
35 print(root.val,root.left.val,root.right.val)
36
37 root = s.trimBST(root,1,2)
38
39 print(root, root.left, root.right)