树的子结构--判断B是不是A的子树

 public boolean HasSubtree(TreeNode root1,TreeNode root2) {
        boolean sign=false;
        if (root2==null||root1==null){
            return false;
        }
        if (root1.val==root2.val){
            sign=judgeChild(root1,root2);
        }
        if (!sign){
           return HasSubtree(root1.left,root2)||HasSubtree(root1.right,root2);
        }
           return sign;
    }

    private boolean judgeChild(TreeNode root1, TreeNode root2) {
        if (root1==null&&root2!=null){
            return false;
        }
        if (root2==null){
            return true;
        }
        if (root1.val!=root2.val){
            return false;
        }
     return judgeChild(root1.left,root2.left)&&judgeChild(root1.right,root2.right);

    }