19、二叉树的镜像

越来越喜欢递归了！

/**public class TreeNode {    int val = 0;    TreeNode left = null;    TreeNode right = null;    public TreeNode(int val) {        this.val = val;    }}*/public class Solution {    public void Mirror(TreeNode root) {        if(root == null) return;        //if(root.left == null && root.right == null) return;        if(root.left != null) Mirror(root.left);        if(root.right != null) Mirror(root.right);        TreeNode temp = root.left;        root.left = root.right;        root.right = temp;    }}