write a go solution for Description:
There are n boxes placed in a line. The boxes are numbered from 1 to n. Some boxes contain one ball inside of them, the rest are empty. At least one box contains a ball and at least one box is empty.

In one move, you have to choose a box with a ball inside and an adjacent empty box and move the ball from one box into another. Boxes i and i+1 for all i from 1 to n-1 are considered adjacent to each other. Boxes 1 and n are not adjacent.

How many different arrangements of balls exist after exactly k moves are performed? Two arrangements are considered different if there is at least one such box that it contains a ball in one of them and doesn't contain a ball in the other one.

Since the answer might be pretty large, print its remainder modulo 10^9+7.

Input Format:
The first line contains two integers n and k (2<=n<=1500; 1<=k<=1500) — the number of boxes and the number of moves.

The second line contains n integers a_1,a_2,...,a_n (a_iin0,1) — 0 denotes an empty box and 1 denotes a box with a ball inside. There is at least one 0 and at least one 1.

Output Format:
Print a single integer — the number of different arrangements of balls that can exist after exactly k moves are performed, modulo 10^9+7.

Note:
In the first example, there are the following possible arrangements:

- 0 1 1 0 — obtained after moving the ball from box 1 to box 2;
- 1 0 0 1 — obtained after moving the ball from box 3 to box 4;
- 1 1 0 0 — obtained after moving the ball from box 3 to box 2.

In the second example, there are the following possible arrangements:

- 1 0 1 0 — three ways to obtain that: just reverse the operation performed during the first move;
- 0 1 0 1 — obtained from either of the first two arrangements after the first move.. Output only the code with no comments, explanation, or additional text.