1126 求递推序列的第N项
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2022-04-08 09:17:57
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#include<iostream>
#include<algorithm>
#include<vector>
#include<cstdio>
typedef long long ll;
using namespace std;
typedef vector<ll> vec;
typedef vector<vec> mat;
ll n;
mat mul(mat &A, mat &B){
mat C(A.size(), vec(B[0].size(), 0));
for(int i = 0; i < A.size(); ++i){
for(int j = 0; j < B.size(); ++j){
for(int k = 0; k < B[0].size(); ++k){
C[i][j] = (C[i][j] + A[i][k] * B[k][j]);
C[i][j] %= 7;
}
}
}
return C;
}
mat modPow(mat A, ll n){
mat B(A.size(), vec(A.size()));
for(int i = 0; i < A.size(); ++i) B[i][i] = 1;
while(n){
if(n&1){
B = mul(B, A);
}
A = mul(A, A);
n >>= 1;
}
return B;
}
void solve(ll a, ll b){
mat A(2, vec(2));
A[0][0] = a;
A[0][1] = b;
A[1][0] = 1;
A[1][1] = 0;
A = modPow(A, n - 2);
printf("%lld\n", (A[0][0] + A[0][1] + 7) % 7);
}
int main(){
ll a, b;
scanf("%lld%lld%lld", &a, &b, &n);
solve(a, b);
return 0;
}
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