$(10$ points$)$ Let A and $B$ be sets such that each has $n$ positive integers in a non$-$decreasing order. We want to

compute the set $C$ such that ainC if and only if a appears either $($i$)$ in both A and $B,$ or $($ii$)$ more than once

in $A$ or $B.$ For example, if $A=\{1,3,3,5,7\}$ and $B=\{2,4,5,6,8\},$ then $C=\{3,5\}.$ Give an $O(n)$ time

algorithm for the problem.