669. Trim a Binary Search Tree

简单题目，BST的搜索遍历

/** * 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==NULL)            return root;        while(root!=NULL&&((root->val)<L||(root->val)>R)){            if((root->val)<L)                root = root-> right;            else if((root->val)>R)                root = root-> left;            else            {}        }        if (root==NULL)              return NULL;        else{            root->left = trimBST(root->left, L,R);            root->right = trimBST(root->right, L, R);            return root;        }    }};