树的子结构

Description：输入两棵二叉树A，B，判断B是不是A的子结构。

/**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;        return isSubtree(root1, root2) || HasSubtree(root1.left, root2) || HasSubtree(root1.right, root2);    }        public boolean isSubtree(TreeNode root1,TreeNode root2) {        if (root2 == null) return true;        if (root1 == null) return false;        if (root2.val == root1.val) {            return isSubtree(root1.left, root2.left) && isSubtree(root1.right, root2.right);        }        return false;    }}