力扣-669题修剪二叉搜索树（C++）- dfs

题目链接：https://leetcode-cn.com/problems/trim-a-binary-search-tree/
题目如下：

/**
 * 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) return nullptr;
        
        if(root->val<low){
            //寻找符合区间的节点
            TreeNode* right=trimBST(root->right,low,high);
            return right;
        }
        if(root->val>high){
            //寻找符合区间的节点
            TreeNode* left=trimBST(root->left,low,high);
            return left;
        }

        root->left=trimBST(root->left,low,high);
        root->right=trimBST(root->right,low,high);

        return root;
    }
};