Practice Second Minimum Node In a Binary Tree

Read the task, work through the examples, and check your approach against the constraints. Use the original LeetCode task for coding and submissions.

Easy#671

LeetCode Problem

Second Minimum Node In a Binary Tree

Tree Depth-First Search Binary Tree

Problem Statement

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.

Source: Second Minimum Node In a Binary Tree on LeetCode. Use the original task for its coding environment and submissions.

Examples

# Example 1

Input

root = [2,2,5,null,null,5,7]

Output

# Example 2

Input

root = [2,2,2]

Output

-1

Constraints

The number of nodes in the tree is in the range [1, 25].

1 <= Node.val <= 2^31 - 1

root.val == min(root.left.val, root.right.val) for each internal node of the tree.

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