[一起来刷leetcode吧][6]--No.669 Trim a Binary Search Tree

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这是leetcode的第669题--Trim a Binary Search Tree

  题目 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.   思路   

show me the code

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 L>root.val:
            return self.trimBST(root.right,L,R)
        elif R<root.val:
            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