OJ-Problems-Source/HDOJ/4602_autoAC.cpp

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#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
const int mod=1000000007;
struct Matrix{
long long arr[2][2];
};
Matrix init,unit;
int n,k;
long long num[2][2]={{4,-4},{1,0}};
void Init(){
for(int i=0;i<2;i++)
for(int j=0;j<2;j++){
init.arr[i][j]=num[i][j];
unit.arr[i][j]=(i==j)?1:0;
}
}
Matrix Mul(Matrix a,Matrix b){
Matrix c;
for(int i=0;i<2;i++)
for(int j=0;j<2;j++){
c.arr[i][j]=0;
for(int k=0;k<2;k++)
c.arr[i][j]=(c.arr[i][j]%mod+a.arr[i][k]*b.arr[k][j]%mod+mod)%mod;
c.arr[i][j]%=mod;
}
return c;
}
Matrix Pow(Matrix a,Matrix b,int k){
while(k){
if(k&1){
b=Mul(a,b);
}
a=Mul(a,a);
k>>=1;
}
return b;
}
int main(){
int t;
scanf("%d",&t);
while(t--){
scanf("%d%d",&n,&k);
Init();
if(k>n){
printf("0\n");
continue;
}
int tmp=n-k+1;
if(tmp==1){
printf("1\n");
continue;
}
if(tmp==2){
printf("2\n");
continue;
}
if(tmp==3){
printf("5\n");
continue;
}
Matrix res=Pow(init,unit,tmp-3);
long long ans=(res.arr[0][0]*5+res.arr[0][1]*2)%mod;
cout<<ans<<endl;
}
return 0;
}