The naive approach, visit all nodes and compare a value in each node. A better approach is to use the definition of a binary search tree.

How to find minimum value in a Binary Search Tree (BST)

Given a <code>binary search tree</code>, return the <code>minimum value</code>. Return <code>-1</code> if there is no <code>minimum value</code>.
 
<code>Example 1</code>
<pre><code>Input: 4 
 / \
 2 5

Output: 2
</code></pre>
<code>Example 2</code>
<pre><code>Input: 1 
 \ 
 3 

Output: 1
</code></pre>

74: Minimum value in a binary search tree