I am having trouble understanding the last part of the editorial:

" For each value *k* , we will compute the new prices, sort them and pick the minimum *k* prices to find the best minimum cost for *k* items. "

How can we prove this ? That for each value of k, it’s cost will be minimum when we sort it and find the minimum value subarray of k elements ?

Since the cost also depends on the index of the value ie cost = v[i]+index[v[i]]*k

Shouldn’t we find all the possible sub sequence of length k, and then find the minimum among them?