Solution.java

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    private Set<TreeNode> vis = new HashSet<>();

    public TreeNode correctBinaryTree(TreeNode root) {
        return dfs(root);
    }

    private TreeNode dfs(TreeNode root) {
        if (root == null || vis.contains(root.right)) {
            return null;
        }
        vis.add(root);
        root.right = dfs(root.right);
        root.left = dfs(root.left);
        return root;
    }
}