Second Minimum Node In A Binary Tree is an example of tree problems. In this post we will see how we can solve in Javascript.

Problem Description

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.

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.

Example 1:

Input:
      2
     / \
    2   5
       / \
      5   7
 
Output: 5

Explanation: The smallest value is 2, the second smallest value is 5. 

Example 2:

Input:
      2
     / \
    2   2
 
Output: -1

Explanation: The smallest value is 2, but there isn't any second smallest value.

Solution: Please check the main.js snippet for the solution. If you have different approach in mind or have any suggestion for this implementation feel free to share in the comment below. Thanks!