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 Python (3.4.3) (judge verdict: Time Limit Exceeded)

N, A = map(int, input().split())
X = list(map(int, input().split()))
L = max(X)
L = max(L, A)

dp = [[[0 for _ in range((N+1)*(L+1))] for _ in range(N+1)] for _ in range(N+1)]
dp[0][0][0] = 1

for j in range(1, N+1):
    for k in range(N+1):
        for s in range((N+1)*(L+1)):
            if s < X[j-1]:
                dp[j][k][s] = dp[j-1][k][s]
            if k >= 1 and s >= X[j-1]:
                dp[j][k][s] = dp[j-1][k][s] + dp[j-1][k-1][s-X[j-1]]
ans = 0
for k in range(1, N+1):
    ans += dp[N][k][k*A]
print(ans)