Minimum Absolute Difference in BST

530. Minimum Absolute Difference in BST

Given a binary search tree with non-negative values, find the minimum absolute difference between values of any two nodes.
Example:

Input:

   1
    \
     3
    /
   2

Output:  
1

Explanation:  
The minimum absolute difference is 1, which is the difference between 2 and 1 (or between 2 and 3).  

Note: There are at least two nodes in this BST.

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {  
    int min = Integer.MAX_VALUE;
    TreeNode prev = null;

    public int getMinimumDifference(TreeNode root) {
        if (root == null) {
            return min;
        }

        getMinimumDifference(root.left);

        if (prev != null) {
            min = Math.min(min, root.val - prev.val);
        }
        prev = root;

        getMinimumDifference(root.right);

        return min;
    }
}

Hope this helps,
Michael