1000. Minimum Cost to Merge Stones

There are n piles of stones arranged in a row. The ith pile has stones[i] stones. A move consists of merging exactly k consecutive piles into one pile, and the cost of this move is equal to the total number of stones in these k piles. Return the minimum cost to merge all piles of stones into one pile. If it is impossible, return -1. Example 1: Input: stones = [3,2,4,1], k = 2 Output: 20 Expl