is subtree or not

判断一个树是不是另一个树的子树

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

    public boolean issubtree(TreeNode big, TreeNode small) {
        if (big != null && small != null) {
            if (big.val == small.val) {
                if (issametree(big, small))
                    return true;
            }
            else {
                if (big.left != null && issubtree(big.left, small)) {
                    return true;
                }
                if (big.right != null && issubtree(big.right, small)) {
                    return true;
                }
            }
        }
        return false;
    }

    public static void main(String[] args) {
        SameTreeSubTree s = new SameTreeSubTree();
        TreeNode tn1 = new TreeNode(1);
        TreeNode tn2 = new TreeNode(2);
        TreeNode tn3 = new TreeNode(3);
        TreeNode tn4 = new TreeNode(4);
        TreeNode tn5 = new TreeNode(5);
        tn1.left = tn2;
        tn1.right = tn3;
        tn4.left = tn5;
        System.out.println(s.issubtree(tn1, tn2));
        System.out.println(s.issubtree(tn1, tn4));
    }