TopCoder - 15135 LongPalindromes

#include<bits/stdc++.h>
#define reg register int
#define il inline
#define fi first
#define se second
#define mk(a,b) make_pair(a,b)
#define numb (ch^‘0‘)
#define pb push_back
#define solid const auto &
#define enter cout<<endl
#define pii pair<int,int>
using namespace std;
typedef long long ll;
template<class T>il void rd(T &x){
    char ch;x=0;bool fl=false;while(!isdigit(ch=getchar()))(ch==‘-‘)&&(fl=true);
    for(x=numb;isdigit(ch=getchar());x=x*10+numb);(fl==true)&&(x=-x);}
template<class T>il void output(T x){if(x/10)output(x/10);putchar(x%10+‘0‘);}
template<class T>il void ot(T x){if(x<0) putchar(‘-‘),x=-x;output(x);putchar(‘ ‘);}
template<class T>il void prt(T a[],int st,int nd){for(reg i=st;i<=nd;++i) ot(a[i]);putchar(‘\n‘);}
namespace Modulo{
const int mod=1e9+7;
il int ad(int x,int y){return x+y>=mod?x+y-mod:x+y;}
il int sub(int x,int y){return ad(x,mod-y);}
il int mul(int x,int y){return (ll)x*y%mod;}
il void inc(int &x,int y){x=ad(x,y);}
il void inc2(int &x,int y){x=mul(x,y);}
il int qm(int x,int y=mod-2){int ret=1;while(y){if(y&1) ret=mul(x,ret);x=mul(x,x);y>>=1;}return ret;}
template<class ...Args>il int ad(const int a,const int b,const Args &...args) {return ad(ad(a,b),args...);}
template<class ...Args>il int mul(const int a,const int b,const Args &...args) {return mul(mul(a,b),args...);}
}
using namespace Modulo;
const int N=110;
int n,m;
struct tr{
    int a[N][N];
    tr(){memset(a,0,sizeof a);}
    void init(){
        for(reg i=0;i<=m;++i){
            a[i][i]=1;
        }
    }
    tr friend operator *(const tr &a,const tr &b){
        tr c;
        for(reg k=0;k<=m;++k){
            for(reg i=0;i<=m;++i){
                for(reg j=0;j<=m;++j){
                    inc(c.a[i][j],mul(a.a[i][k],b.a[k][j]));
                }
            }
        }
        return c;
    }
}S,A,B,C;
tr qm(tr A,ll y){
    tr ret;
    memset(ret.a,0,sizeof ret.a);
    ret.init();
    while(y){
        if(y&1) ret=ret*A;
        A=A*A;
        y>>=1;
    }return ret;
}
class LongPalindromes{
public:
    int count(int T,string s){
        int n=s.length();
        if(n==1) return qm(2,T);
        m=n*2;
        //0~n-1
        //n~m-1
        //a[0][m]=1
        for(reg i=0;i<=n-1;++i){
            A.a[i][i]=1;
            A.a[(i+1)%n][i]=1;
            A.a[i][i+n]=1;
        }
        A.a[m][m]=1;
        B.init();
        for(reg len=1;len<=n;++len){
            C=A;
            for(reg i=0;i<n;++i){
                C.a[(i+1)%n+n][i]=sub((s[i]==s[(i+len-1)%n]),1);
                C.a[m][i]=(s[i]==s[(i+len-1)%n]);
            }
            B=B*C;
        }
        S.a[0][m]=1;
        S=S*qm(B,T);
        // printf("%d\n",
        return ad(S.a[0][0],1);
    }
};