import sys, os, io
input = io.BytesIO(os.read(0, os.fstat(0).st_size)).readline
def matmul(a, b, n):
c = []
for i in range(n):
for j in range(n):
x = 0
for k in range(n):
x += a[n * i + k] * b[n * k + j] % mod
x %= mod
c.append(x)
return c
n, k = map(int, input().split())
a = list(map(int, input().split()))
mod = pow(10, 9) + 7
s = n - sum(a)
m = min(s, n - s) + 1
x = [0] * (m * m)
b = list(a)
b.sort()
for i in range(m):
for j in range(n):
for l in range(j + 1, n):
if b[j] == b[l]:
x[i * m + i] += 1
continue
b[j], b[l] = b[l], b[j]
c = 0
for u in range(s):
c += b[u]
x[i * m + c] += 1
b[j], b[l] = b[l], b[j]
if i ^ (m - 1):
b[i], b[-i - 1] = b[-i - 1], b[i]
y = [min(i % (m + 1), 1) ^ 1 for i in range(m * m)]
z = pow(n * (n - 1) // 2, k, mod)
invz = pow(z, mod - 2, mod)
p = 1
while k:
if k & p:
y = matmul(x, y, m)
k ^= p
x = matmul(x, x, m)
p *= 2
ans = y[sum(a[:s]) * m] * invz % mod
print(ans)#include<bits/stdc++.h>
using namespace std;
using ll=long long;
const ll mod=1e9+7;
ll qpow(ll a,ll b){ll res=1;while(b){if(b&1)res=res*a%mod;a=a*a%mod,b>>=1;}return res;}
const int N=102;
int n,k,m,x,a[N];
int A[N],B[N],C[N];
struct mul{
int n;
ll g[N][N];
mul(int n_){n=n_;memset(g,0,sizeof g);}
mul operator *(mul &y){
mul c(y.n);
for(int i=0;i<n;i++)
for(int k=0;k<n;k++)
for(int j=0;j<n;j++)
c.g[i][j]=(c.g[i][j]+g[i][k]*y.g[k][j])%mod;
return c;
}
};
inline mul ksm(mul a,ll b){
mul res(a.n);
for(int i=0;i<m+1;i++)res.g[i][i]=1;
while(b){
if(b&1)res=res*a;
a=a*a,b>>=1;
}
return res;
}
int main(){
scanf("%d%d",&n,&k);
for(int i=1;i<=n;i++)scanf("%d",&a[i]),m+=!a[i];
for(int i=0;i<=m;i++)A[i]=(m-i)*(m-i)%mod,B[i]=i*(n-2*m+i)%mod,C[i]=((n-1)*n/2-A[i]+mod-B[i]+mod)%mod;
mul ans(m+1);
ans.g[0][0]=C[0],ans.g[1][0]=A[0];
ans.g[m][m]=C[m],ans.g[m-1][m]=B[m];
for(int i=1;i<m;i++)ans.g[i][i]=C[i],ans.g[i-1][i]=B[i],ans.g[i+1][i]=A[i];
ans=ksm(ans,k);
ll cnt=0;
for(int i=1;i<=m;i++)x+=!a[i];
for(int i=0;i<=m;i++)cnt=(cnt+ans.g[i][x])%mod;
printf("%lld",ans.g[m][x]*qpow(cnt,mod-2)%mod);
return 0;
}
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1316A - Grade Allocation | 838A - Binary Blocks |
1515D - Phoenix and Socks | 1624D - Palindromes Coloring |
1552F - Telepanting | 1692G - 2Sort |
1191A - Tokitsukaze and Enhancement | 903A - Hungry Student Problem |
52B - Right Triangles | 1712A - Wonderful Permutation |
1712D - Empty Graph | 1712B - Woeful Permutation |
1712C - Sort Zero | 1028B - Unnatural Conditions |
735B - Urbanization | 746C - Tram |
1278B - A and B | 1353D - Constructing the Array |