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

/**
 * Second Minimum Node In a Binary Tree
 *
 * 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.
 */

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number}
 */
var findSecondMinimumValue = function(root) {
  if (!root) {
    return -1;
  }

  if (!root.left && !root.right) {
    return -1;
  }

  var left = root.left.val;
  var right = root.right.val;

  if (left === root.val) {
    left = findSecondMinimumValue(root.left);
  }

  if (right === root.val) {
    right = findSecondMinimumValue(root.right);
  }

  if (left !== -1 && right !== -1) {
    return Math.min(left, right);
  }

  if (left !== -1) {
    return left;
  }

  return right;
};

export { findSecondMinimumValue };