【BZOJ4870】组合数问题 [矩阵乘法][DP]

#include<iostream>  
#include<string>  
#include<algorithm>  
#include<cstdio>  
#include<cstring>  
#include<cstdlib>  
#include<cmath>
using namespace std;
typedef long long s64;

const int ONE = 55;

int n,MOD,num,r;

inline s64 get()
{
        s64 res=1,Q=1;  char c;
        while( (c=getchar())<48 || c>57)
        if(c==‘-‘)Q=-1;
        if(Q) res=c-48; 
        while((c=getchar())>=48 && c<=57) 
        res=res*10+c-48;
        return res*Q; 
}

struct Matrix
{
        s64 v[ONE][ONE];
        friend Matrix operator *(Matrix a,Matrix b)
        {
            Matrix record;
            for(int i=0;i<num;i++)
            for(int j=0;j<num;j++)
            {
                record.v[i][j]=0;
                for(int k=0;k<num;k++)
                record.v[i][j] = (s64)(record.v[i][j] + a.v[i][k]*b.v[k][j] % MOD) % MOD;
            }
            return record;
        }
};
Matrix B,Ans;

Matrix Quickpow(Matrix a,s64 b)
{
        Matrix res;
        for(int i=0;i<num;i++) res.v[i][i] = 1;
        while(b)
        {
            if(b&1) res = res*a;
            a = a*a;
            b>>=1;
        }
        return res;
}

int main()
{
        n=get();    MOD=get();    num=get();    r=get();
        for(int i=0;i<num;i++)
        {
            B.v[i][i]++;
            B.v[((i-1)%num+num)%num][i]++;
        }
        
        Ans = Quickpow(B, (s64)n*num);
        
        cout<<Ans.v[0][r];
        
}