6461：Tak and Cards(数位DP)
6461: Tak and Cards
时间限制: 1 Sec 内存限制: 128 MB提交: 173 解决: 63
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题目描述
Tak has N cards. On the i-th (1≤i≤N) card is written an integer xi. 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≤N≤50
1≤A≤50
1≤xi≤50
N,A,xi are integers.
Partial Score
200 points will be awarded for passing the test set satisfying 1≤N≤16.
输入
The input is given from Standard Input in the following format:N A
x1 x2 … xN
输出
Print the number of ways to select cards such that the average of the written integers is exactly A.样例输入
4 8
7 9 8 9
样例输出
5
提示
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.
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