如题，样例没事，但是全部WA掉了，求各位大神帮助！

#include<iostream>
using namespace std;
typedef long long ll;
ll n,k;
struct matrix{
    ll mt[201][201];
    void output(){for(ll i=1;i<=n;i++){for(ll j=1;j<=n;j++)cout<<mt[i][j]<<" ";cout<<endl;}}
};

const ll mod=1000000007ll;
matrix operator*(matrix x,matrix y){
    matrix z;
    for(ll i=1;i<=n;i++){
        for(ll j=1;j<=n;j++){
            for(ll k=1;k<=n;k++)z.mt[j][k]=(x.mt[j][i]*y.mt[i][k]%mod+z.mt[j][k])%mod;
        }
    }
    return z;
}
matrix fpow(matrix b,ll p){
    if(p==1)return b;
    matrix ans=fpow(b,(p>>1));
    ans=ans*ans;
    if(p&1)ans=ans*b;
    return ans;
}
matrix a,res;
int main(){
    cin>>n>>k;
    for(ll i=1;i<=n;i++)for(ll j=1;j<=n;j++)cin>>a.mt[i][j];
    res=fpow(a,k);
    res.output();
    return 0;
}