1、前言

2、思路

3、代码

class Solution {
    public TreeNode mirrorTree(TreeNode root) {
        if(root == null){
            return root;
        }
        mirrorTree(root.left);
        mirrorTree(root.right);

        TreeNode temp = root.left;
        root.left = root.right;
        root.right = temp;

        return root;
    }
}