C++ :

#include<bits/stdc++.h>
using namespace std;

#define LL long long

const LL N=51,M=2501;

LL n,k,a[N],f[N][M][N];

int main(){
	scanf("%lld%lld",&n,&k);
	for(LL i=1;i<=n;i++) scanf("%lld",&a[i]);
	for(LL i=0;i<N;i++) f[i][0][0]=1;
	for(LL i=1;i<=n;i++){
		for(LL j=0;j<M;j++){
			for(LL k=0;k<=i;k++){
				f[i][j][k]=f[i-1][j][k];
				if(j>=a[i]&&k>=1) f[i][j][k]+=f[i-1][j-a[i]][k-1];
			}
		}
	}
	LL ans=0;
	for(LL i=1;i<=n;i++){
		for(LL j=0;j<i;j++){
			LL sum=(j+1)*k-a[i];
			if(sum>=0) ans+=f[i-1][sum][j];
		}
	}
	printf("%lld\n",ans);
}

Python :

# coding=utf-8
N, A = map(int, input().split())
Xs = list(map(int, input().split()))

Ys = [X-A for X in Xs]
sumPos = sumNeg = 0
for Y in Ys:
    if Y >= 0:
        sumPos += Y
    else:
        sumNeg += Y
#print('# sumPos:', sumPos, '/ sumNeg:', sumNeg)

LLL = sumPos - sumNeg + 1

dp = [0] * (LLL+1)
dp[0] = 1
for Y in Ys:
    dp2 = dp[:]
    for s in range(sumNeg, sumPos+1):
        dpNow = dp[s]
        if dpNow == 0:
            continue
        s2 = s+Y
        dp2[s2] += dpNow
    dp = dp2
#    print('# Y:', Y, '/ dp:', dp)

ans = dp[0] - 1
print(ans)