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）

思路：用了2种递归

/**public class TreeNode {    int val = 0;    TreeNode left = null;    TreeNode right = null;    public TreeNode(int val) {        this.val = val;    }}*/public class Solution {    public boolean HasSubtree(TreeNode root1,TreeNode root2) {        if(root1 == null || root2 == null)return false;                if(root1.val == root2.val && HasSubtree2(root1, root2))            return true;                    return HasSubtree(root1.left, root2) || HasSubtree(root1.right, root2);    }        public boolean HasSubtree2(TreeNode root1,TreeNode root2) {        if(root2 == null)return true;        if(root1 == null)return false;                return root1.val == root2.val && HasSubtree2(root1.left, root2.left) && HasSubtree2(root1.right, root2.right);    }    }