Leetcode 99. Recover Binary Search Tree

Posted 2023-02-23 zhangwj0101

Question

Two elements of a binary search tree (BST) are swapped by mistake.

Recover the tree without changing its structure.

Code

 TreeNode pre = null;
    TreeNode first = null;
    TreeNode second = null;

    public void recoverTree(TreeNode root) 
        inOrder(root);

        int tmp = first.val;
        first.val = second.val;
        second.val = tmp;
    

    public void inOrder(TreeNode root) 
        if (root == null) 
            return;
        

        inOrder(root.left);
        if (pre != null && pre.val > root.val) 
            if (first == null) 
                first = pre;
                second = root;
             else 
                second = root;
            
        
        pre = root;
        inOrder(root.right);