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
思路：递归（Recursion）
1.从根节点root开始，若当前节点值小于L，则砍掉左子树，保留右子树，对右子树进行剪枝；
2.若当前节点值大于R，则砍掉右子树，保留左子树，对左子树进行剪枝；
3.若当前节点值位于[L,R]之间，则递归，分别对左、右子树进行剪枝；
# Definition for a binary tree node. # class TreeNode: # def __init__(self, x): # self.val = x # self.left = None # self.right = None class Solution: 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
669. Trim a Binary Search Tree (Easy)
原文：http://www.cnblogs.com/yancea/p/7506674.html