求问 leetcode 上的一道 BST 题。

我的代码如下

/**
 * 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) {
        TreeNode res = new TreeNode(Integer.MAX_VALUE);
        TreeNode pre = null;
        inOrder(root, res, pre);
        return res.val;
    }
    
    private void inOrder(TreeNode node, TreeNode k, TreeNode pre) {
        if (node==null) return;
        inOrder(node.left, k, pre);
        if (pre!=null) k.val = Math.min(k.val, node.val-pre.val);
        pre = node;
        inOrder(node.right, k, pre);
    }
    
}

讨论区网友的代码如下

class Solution {
    
    // do a inorder traversal
    // compare current val with previous val
    // update answer
    
    private Integer prev;
    private int ans;
    
    public int getMinimumDifference(TreeNode root) {
        ans = Integer.MAX_VALUE;
        inorder(root);
        return ans;
    }
     
    private void inorder(TreeNode root) {
        if (root == null) return;
        inorder(root.left);
        if (prev != null)
            ans = Math.min(ans, root.val - prev);
        prev = root.val;
        inorder(root.right);
    }
}

部分测试通不过，自己实在找不出错误了，希望大家能帮忙看看。感激不尽