题目地址:https://leetcode.com/problems/trim-a-binary-search-tree/description/
题目描述
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
题目大意
给定[L,R]区间,进行BST裁剪。只要数值不在该区间的节点,全部都删除。返回的结果应该仍然是个BST.
解题方法
递归
想法很简单了,如果root的值比R大,说明root以及其所有右节点都不在这个区间内,向左边搜索。如果root的值比L小,,说明root以及其所有左节点都不在这个区间内,向右边搜索。如果root正好在这个区间内,那么分别对它的左右子树进行裁剪就好了。
# 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 > R:
return self.trimBST(root.left, L, R)
elif root.val < L:
return self.trimBST(root.right, L, R)
else:
root.left = self.trimBST(root.left, L, R)
root.right = self.trimBST(root.right, L, R)
return root
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