TRIM_A_BINARY_SEARCH_TREE.cpp

/**
 * 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 = root->right;
        }
        else if(root->val > R){
            root = root->left;
        }
        
        return root;
    }
};