LeetCode25|二叉树的镜像

例如输入：

     4
   /   \
  2     7
 / \   / \
1   3 6   9
镜像输出：

     4
   /   \
  7     2
 / \   / \
9   6 3   1

public class MirronTreeTest {
    public static void main(String[] args) {
        TreeNode t1 = new TreeNode(4);
        TreeNode t2 = new TreeNode(2);
        TreeNode t3 = new TreeNode(7);
        TreeNode t4 = new TreeNode(1);
        TreeNode t5 = new TreeNode(3);
        TreeNode t6 = new TreeNode(6);
        TreeNode t7 = new TreeNode(9);
        t1.left = t2;
        t1.right = t3;
        t2.left = t4;
        t2.right = t5;
        t3.left = t6;
        t3.right = t7;
        TreeNode treeNode = mirrorTree(t1);
        System.out.println("treeNode = " + treeNode);

    }

    public static TreeNode mirrorTree(TreeNode root) {
        if (root == null) {
            return root;
        }
        TreeNode leftNode = mirrorTree(root.left);
        TreeNode rightNode = mirrorTree(root.right);
        root.right = leftNode;
        root.left = rightNode;
        return root;
    }
}