# 1000. Minimum Cost to Merge Stones

<https://leetcode.com/problems/minimum-cost-to-merge-stones>

## Description

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
**Explanation:** We start with [3, 2, 4, 1].
We merge [3, 2] for a cost of 5, and we are left with [5, 4, 1].
We merge [4, 1] for a cost of 5, and we are left with [5, 5].
We merge [5, 5] for a cost of 10, and we are left with [10].
The total cost was 20, and this is the minimum possible.
```

**Example 2:**

```
**Input:** stones = [3,2,4,1], k = 3
**Output:** -1
**Explanation:** After any merge operation, there are 2 piles left, and we can't merge anymore.  So the task is impossible.
```

**Example 3:**

```
**Input:** stones = [3,5,1,2,6], k = 3
**Output:** 25
**Explanation:** We start with [3, 5, 1, 2, 6].
We merge [5, 1, 2] for a cost of 8, and we are left with [3, 8, 6].
We merge [3, 8, 6] for a cost of 17, and we are left with [17].
The total cost was 25, and this is the minimum possible.
```

**Constraints:**

* `n == stones.length`
* `1 <= n <= 30`
* `1 <= stones[i] <= 100`
* `2 <= k <= 30`

## ac

```java
```
