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

这个题和BST中最小距离没有区别

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public int getMinimumDifference(TreeNode root) {
        if(root == null)
            return 0;

        Stack<TreeNode> stack = new Stack<TreeNode>();
        TreeNode p = root;
        while(p != null) {
            stack.push(p);
            p = p.left;
        }

        int res = Integer.MAX_VALUE;
        Integer last = null;

        while(stack.size() > 0) {
            TreeNode temp = stack.pop();
            if(last == null) {
                last = temp.val;
            } else {
                res = Math.min(res, temp.val - last);
                last = temp.val;
            }

            if(temp.right != null) {
                p = temp.right;
                while(p != null) {
                    stack.push(p);
                    p = p.left;
                }
            }
        }

        return res;
    }
}