Can someone please help me out with the solution of this problem "Natsya decided to visit a local store, which has n items. The i-th item has price a[i]

She has to buy k items out of the n items such that total price of all the items bought is minimum.

In how ways she can buy k items such that the overall price is minimum?"

1<=k<=n<=50 a[i]<=n

I have tried to solve it but it is failing in some hidden cases Code.