#include<cstdio>
#define fo(i,x,y) for(int i = x;i <= y;++i)
#define fd(i,x,y) for(int i = x;i >= y;--i)
#define p 1000000007
int n,m,x,c[310],iv[310],f[310],ef[310],w[310],ifac[310],fac[310];
int ksm(int x,int y)
{
	int res = 1;
	for(;y;y >>= 1,x = 1ll * x * x % p) if(y & 1) res = 1ll * res * x % p;
	return res;
}
int main()
{
	scanf("%d%d",&n,&m);
	fo(i,1,n) scanf("%d",&x),++c[x];
	fac[0] = 1;
	fo(i,1,n) fac[i] = 1ll * fac[i - 1] * i % p;
	ifac[n] = ksm(fac[n],p - 2);
	fd(i,n - 1,0) ifac[i] = 1ll * ifac[i + 1] * (i + 1) % p;
	fo(i,1,n) iv[i] = 1ll * ifac[i] * fac[i - 1] % p;
	fo(i,1,m) w[i] = 1ll * ksm(i,i - 1) * ifac[i] % p;
	int ans = 1;
	fo(i,1,n) if(c[i])
	{
		int C = c[i];
		fo(j,1,C) f[j] = (j <= m) ? 1ll * (n - C) * w[j] % p : 0;
		ef[0] = 1;
		fo(j,1,C)
		{
			ef[j] = 0;
			fo(k,0,j - 1) ef[j] = (ef[j] + 1ll * ef[k] * f[j - k] % p * (j - k)) % p;
			ef[j] = 1ll * ef[j] * iv[j] % p;
		}
		int res = 0;
		fo(j,1,C) res = (res + 1ll * j * w[j] % p * n % p * ef[C - j]) % p;
		ans = 1ll * ans * res % p * fac[C - 1] % p;
	}
	printf("%lld\n",1ll * ans * ksm(n,(p - 2) * 2) % p);
}