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: Runtime Error)

N, A = map(int, input().split())  # N枚数のカード, 平均をAにしたい
X = tuple(map(int, input().split()))  # N枚のカードの中身

dp = [[[0]*(50*N+1) for _ in range(N+1)] for _ in range(N+1)]

dp[0][0][0] = 1  # 0枚の中から0枚選んで合計が0になる選び方が1通りある

for i in range(N):
    for j in range(N+1):
        for s in range(50*N+1):
            if s >= X[i]:  # 今見ているのはX[i], これをどうするかで遷移先を変更する
                dp[i+1][j+1][s] += dp[i][j][s-X[i]]  # 追加する余裕がある場合は追加する
            dp[i+1][j][s] += dp[i][j][s]  # 何も追加しない
ans = 0
for i in range(1, N+1):
    ans += dp[N][i][i*A]
print(ans)