I think this problem is not very hard and it's interesting.
Description: You are given $$$2$$$ arrays $$$a$$$ and $$$b$$$ and the length of them is $$$n$$$.
$$$1$$$, $$$3$$$, $$$5$$$, ......, $$$2 * n - 1$$$ is in $$$a$$$.
$$$2$$$, $$$4$$$, $$$6$$$, ......, $$$2 * n$$$ is in $$$b$$$.