树的子结构

输入两棵二叉树A，B，判断B是不是A的子结构。（ps：我们约定空树不是任意一个树的子结构）

public class Solution {
     public boolean HasSubtree(TreeNode root1, TreeNode root2) {
                boolean result = false;
                if (root2 != null && root1 != null) {
                    if(root1.val == root2.val){
                        result = doesTree1HaveTree2(root1,root2);
                    }
                    if (!result) {
                        result = HasSubtree(root1.left,root2);
                    }          
                    if (!result) {
                        result = HasSubtree(root1.right,root2);
                       }
                    }
                return result;
            }
         
            public boolean doesTree1HaveTree2(TreeNode node1, TreeNode node2) {
                if (node2 == null) {
                    return true;
                }
                if (node1 == null) {
                    return false;
                }
                if (node1.val != node2.val) {  
                        return false;
                }
                return doesTree1HaveTree2(node1.left,node2.left) && doesTree1HaveTree2(node1.right,node2.right);
            }
}