Camila and Books

This problem can be solved by $DP$. For each type $i$, Camila has three choices $-$ buy $i-$th type, buy $n+1-i-$th type or skip both. So, if we group each $i$ and $n+1-i$ type, there will be total $n/2$ groups. Now, take groups and buy count as state of dp and in each dp state there will be three transitions as skip this group, greedily buy books from $i-$th type and greedily buy books from $n+1-i-$th type and then return the minimum price among them. Overall complexity will be $O(X * K)$.