Two Sum IV - Input is a BST

Problem statement

Given the root of a Binary Search Tree and a target number k, return true if there exist two elements in the BST such that their sum is equal to the given target.

Example 1:

Input: root = [5,3,6,2,4,null,7], k = 9Output: true

Example 2:

Input: root = [5,3,6,2,4,null,7], k = 28Output: false

Constraints:

• The number of nodes in the tree is in the range [1, 104].
• -104 <= Node.val <= 104
• root is guaranteed to be a valid binary search tree.
• -105 <= k <= 105

My solution

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @param {number} k
 * @return {boolean}
 */
var findTarget = function(root, k) {
    const memo = new Map();
    
    let stack = [root]
    
    while (stack.length > 0) {
        const node = stack.shift();
        
        if (!node) {
            return;
        }
        
        const val = node.val;
        const diff = k - val;
        
        // console.log("val", val, ": diff", diff)

        
        if (!memo.has(diff)) {
            // console.log(memo)
            memo.set(val, diff)
        } else {
            return true;
        }
        
        if (node.left) {
            stack.push(node.left)
        }
        
        if (node.right) {
            stack.push(node.right)
        }
    }
    
    return false
};