/**
 * 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)
 * }
 */
/**
 * DFS (level order traversal)
 * Time O(n) | Space O(n)
 * https://leetcode.com/problems/minimum-distance-between-bst-nodes/
 * @param {TreeNode} root
 * @return {number}
 */
var minDiffInBST = function(root) {
    // levelOrderTraversal
    const sortedArr = dfs(root, []);
    
    let min = Infinity;
    for (let i = 1; i < sortedArr.length; i++) {
        min = Math.min(min, sortedArr[i] - sortedArr[i - 1]);
    }
    return min;
};

const dfs = (node, sortedArr) => {
    if (!node) return;

    dfs(node.left, sortedArr);
    sortedArr.push(node.val)
    dfs(node.right, sortedArr);

    return sortedArr;
}