Minimum Distance Between BST Nodes

Description

Given a Binary Search Tree (BST) with the root node root, return the minimum difference between the values of any two different nodes in the tree.

Example :

Input: root = [4,2,6,1,3,null,null]
Output: 1
Explanation:
Note that root is a TreeNode object, not an array.
The given tree [4,2,6,1,3,null,null] is represented by the following diagram:
      4
    /   \
  2      6
 / \    
1   3  

while the minimum difference in this tree is 1, it occurs between node 1 and node 2, also between node 3 and node 2.

Note:

1. The size of the BST will be between 2 and 100.
2. The BST is always valid, each node's value is an integer, and each node's value is different.
3. This question is the same as 530: https://leetcode.com/problems/minimum-absolute-difference-in-bst/

Solution(javascript)

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number}
 */
var minDiffInBST = function(root) {
    let min = Infinity
  let previous = null
  const aux = (node) => {
    if (!node) {
      return
    }
    if (node.left) {
      aux(node.left)
    }
    const possibleMin = Math.abs(node.val - previous)
    if ((previous !== null) && (possibleMin < min)) {
      min = possibleMin
    }
    previous = node.val
    if (node.right) {
      aux(node.right)
    }
  }
  aux(root)
  return min
};