Problem

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.

Example 1:

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

Output: 32

Example 2:

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

Output: 23

Note:

The number of nodes in the tree is at most 10000.

The final answer is guaranteed to be less than 2^31.

Pre analysis

If node value falls between the range, function should return this.val and sum of children, else should return sum of children with same condition

Another solution

1. Iterative Solution

   var rangeSumBST = function(root, L, R) {
   // It basically means sum all values b/w L and R (inclusive)
   var treeStack = [root];
   var sum = 0;
   
   while(treeStack.length) {
       let node = treeStack.pop();
       if(node.val >= L && node.val <= R) {
       sum += node.val;
       }
   
       if(node.left !== null && node.val >= L) {
       treeStack.push(node.left);
       }
   
       if(node.right !== null && node.val <= R) {
       treeStack.push(node.right);
       }
   }
   return sum;
   };