0671-second-minimum-node-in-a-binary-tree.js

/**
 * 671. Second Minimum Node In a Binary Tree
 * https://leetcode.com/problems/second-minimum-node-in-a-binary-tree/
 * Difficulty: Easy
 *
 * Given a non-empty special binary tree consisting of nodes with the non-negative value,
 * where each node in this tree has exactly two or zero sub-node. If the node has two
 * sub-nodes, then this node's value is the smaller value among its two sub-nodes. More
 * formally, the property root.val = min(root.left.val, root.right.val) always holds.
 *
 * Given such a binary tree, you need to output the second minimum value in the set made
 * of all the nodes' value in the whole tree.
 *
 * If no such second minimum value exists, output -1 instead.
 */

/**
 * 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
 * @return {number}
 */
var findSecondMinimumValue = function(root) {
  return root ? (n => n === Infinity ? -1 : n)(traverse(root, root.val)) : -1;
  function traverse(node, min) {
    if (!node) return Infinity;
    if (node.val > min) return node.val;
    return Math.min(traverse(node.left, min), traverse(node.right, min));
  }
};