669. Trim a Binary Search Tree

https://leetcode.com/problems/trim-a-binary-search-tree/

1. Use recursion:

//24 ms    12.9 MB
/**
 * 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;
        root->left = trimBST(root->left, L, R);
        root->right = trimBST(root->right, L, R);
        if(root->val < L || root->val > R){
            if(root->left)
                root = root->left;
            else if(root->right)
                root = root->right;
            else 
                root = NULL;
        }
        return root;
    }
};