Problem:
Score : 300 points

Problem Statement

Tak has N cards. On the i-th (1 \leq i \leq N) card is written an integer x_i.
He is selecting one or more cards from these N cards, so that the average of the integers written on the selected cards is exactly A.
In how many ways can he make his selection?

Constraints

1 \leq N \leq 50

1 \leq A \leq 50

1 \leq x_i \leq 50

N,\,A,\,x_i are integers.

Partial Score

200 points will be awarded for passing the test set satisfying 1 \leq N \leq 16.

Input

The input is given from Standard Input in the following format:

N A
x_1 x_2 ... x_N

Output

Print the number of ways to select cards such that the average of the written integers is exactly A.

Sample Input 1

4 8
7 9 8 9

Sample Output 1

5

The following are the 5 ways to select cards such that the average is 8:

Select the 3-rd card.

Select the 1-st and 2-nd cards.

Select the 1-st and 4-th cards.

Select the 1-st, 2-nd and 3-rd cards.

Select the 1-st, 3-rd and 4-th cards.

Sample Input 2

3 8
6 6 9

Sample Output 2

0

Sample Input 3

8 5
3 6 2 8 7 6 5 9

Sample Output 3

19

Sample Input 4

33 3
3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3

Sample Output 4

8589934591

The answer may not fit into a 32-bit integer.

Solution in PyPy3 (7.3.0) (judge verdict: Accepted)

n,a=map(int,input().split())
x=list(map(int,input().split()))
dp=[[[0]*(2501) for i in range(51)] for j in range(51)]
#dp[i][j][k]は、i番目まででj枚とって総数kとなる取り方
for i in range(n+1):
    dp[i][0][0]=1
for i in range(n):
    for j in range(1,i+2):
        for k in range(1,2501):
            if k-x[i]>=0:
                dp[i+1][j][k]=dp[i][j-1][k-x[i]]+dp[i][j][k]
            else:
                dp[i+1][j][k] = dp[i][j][k]
ans=0
for j in range(1,n+1):
    ans+=dp[n][j][a*j]
print(ans)