题目链接：二叉树的镜像

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 *   public TreeNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param pRoot TreeNode类 
     * @return TreeNode类
     */
    public TreeNode Mirror (TreeNode root) {
        if(root == null) return null;

        TreeNode t = root.left;
        root.left = root.right;
        root.right = t;
        Mirror(root.left);
        Mirror(root.right);
        return root;
    }
}