* Definition for a binary tree node.
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
TreeNode* trimBST(TreeNode* root, int L, int R) {
return root->right? trimBST(root->right, L, R) :NULL;
return root->left? trimBST(root->left, L, R) :NULL;
if(root->left) root->left=trimBST(root->left,L, R);
if(root->right) root->right=trimBST(root->right, L, R);