在C ++中使用引用

Question

我正在编写代码来解决＆＃34;恢复二进制搜索树＆＃34;问题。

https://oj.leetcode.com/problems/recover-binary-search-tree/

首先我编写了这段代码，将 recoverTree 函数中的三个指针放出来：

class Solution {
public:
    TreeNode *pre;
    TreeNode *first;
    TreeNode *second;

    void recoverTree(TreeNode *root) {

        inOrder(root);
        int temp = first->val;
        first->val = second->val;
        second->val = temp;
        return;
    }

    void inOrder(TreeNode *root) {
        if (!root) return;
        inOrder(root->left);
        if (!pre) {
            pre = root;
        } else {
            if (pre->val > root->val) {
                if (!first) first = pre;
                second = root;
            }
            pre = root;
        }
        inOrder(root->right);
    }

};

它工作正常，经过所有测试。然后我想也许不会把三个指针的定义放在函数之外。所以我写了这样的话：

class Solution {
public:

    void recoverTree(TreeNode *root) {
        TreeNode *pre;
        TreeNode *first;
        TreeNode *second;
        inOrder(root, pre, first, second);
        int temp = first->val;
        first->val = second->val;
        second->val = temp;
        return;
    }

    void inOrder(TreeNode *root, TreeNode *&pre, TreeNode *&first, TreeNode *&second) {
        if (!root) return;
        inOrder(root->left, pre, first, second);
        if (!pre) {
            pre = root;
        } else {
            if (pre->val > root->val) {
                if (!first) first = pre;
                second = root;
            }
            pre = root;
        }
        inOrder(root->right, pre, first, second);
    }

};

但这不起作用。我使用引用或其他任何导致错误的内容有什么问题吗？