# 669.Trim a Binary Search Tree

**669.Trim a Binary Search Tree**

难度:Easy

> 给定一个二叉搜索树，同时给定最小边界L 和最大边界 R。通过修剪二叉搜索树，使得所有节点的值在\[L, R]中 (R>=L) 。你可能需要改变树的根节点，所以结果应当返回修剪好的二叉搜索树的新的根节点。

示例 1:

```
输入: 
    1
   / \
  0   2

  L = 1
  R = 2

输出: 
    1
      \
       2
示例 2:

输入: 
    3
   / \
  0   4
   \
    2
   /
  1

  L = 1
  R = 3

输出: 
      3
     / 
   2   
  /
 1
```

简单递归:

```
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode* trimBST(TreeNode* root, int L, int R) {
        if(!root ) return NULL;
        if(root->val < L) 
            return root->right? trimBST(root->right, L, R) :NULL;
        if(root->val > R)
            return root->left? trimBST(root->left, L, R) :NULL;       
        if(root->val==L)
            root->left=NULL;
        if(root->val==R)
            root->right=NULL;
           
       // TreeNode* ptr=root;
        if(root->left) root->left=trimBST(root->left,L, R);
        if(root->right) root->right=trimBST(root->right, L, R);
        return root;
        
        
    }
};
```


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