Given the `root` node of a binary search tree, return the sum of values of all nodes with value between `L` and `R` (inclusive).

The binary search tree is guaranteed to have unique values.

## Examples#

Example1:

``````Input: root = [10,5,15,3,7,null,18], L = 7, R = 15
Output: 32
``````

Example2:

``````Input: root = [10,5,15,3,7,13,18,1,null,6], L = 6, R = 10
Output: 23
``````

## Our solution in Java#

``````/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/
class Solution {
public int rangeSumBST(TreeNode root, int L, int R) {
//output variable
int output = 0;

// Create a stack
Stack<TreeNode> stack = new Stack();
stack.push(root);

// loop through each element
while (!stack.isEmpty()) {

// remove last item from stack
TreeNode node = stack.pop();
// if the node exists
if (node != null) {

// incrememnt output counts
if (L <= node.val && node.val <= R)
output += node.val;

// push if left
if (L < node.val)
stack.push(node.left);

// push if right
if (node.val < R)
stack.push(node.right);
}
}

// return our count
return output;
}
}
``````