解题思路

与专题的删除节点类似，可以参考LC450

代码

Python

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# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def trimBST(self, root: Optional[TreeNode], low: int, high: int) -> Optional[TreeNode]:
        if not root:
            return None 
        
        if root.val < low:
            return self.trimBST(root.right, low, high)
        
        if root.val > high:
            return self.trimBST(root.left, low, high)

        root.left = self.trimBST(root.left, low, high)
        root.right = self.trimBST(root.right, low, high)
        return root

C++

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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    TreeNode* trimBST(TreeNode* root, int low, int high) {
        if (root == NULL) return root;
        if (root != NULL) root->left = trimBST(root->left, low, high);
        if (root != NULL) root->right = trimBST(root->right, low, high);
        if (root->val < low || root->val > high) {
            if (root->left != NULL && root->right != NULL) {
                TreeNode* cur = root->right;
                while (cur->left != NULL) {
                    cur = cur->left;
                }
                cur->left = root->left;
                TreeNode* tmp = root;
                root = root->right;
                delete tmp;
                return root;
            } else if (root->left != NULL) {
                return root->left; 
            } else if (root->right != NULL) {
                return root->right;
            } else {
                return root->left;
            }
        }
        return root;
    }
};

Go

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func trimBST(root *TreeNode, low int, high int) *TreeNode {
    if root == nil {return root}
    if root.Val < low {
        return trimBST(root.Right, low, high)
    }
    if root.Val > high {
        return trimBST(root.Left, low, high)
    }
    root.Left = trimBST(root.Left, low, high)
    root.Right = trimBST(root.Right, low, high)
    return root
}