CodeForces - 450B 矩陣快速冪

#include <cstdio>
#include <cstring>
using namespace std;
const int maxs = 2;
const int mod = 1e9+7;
struct Matrix
{
    int a[maxs][maxs];
    Matrix() {memset(a, 0, sizeof(a));}
    void init()//初始化爲單位矩陣
    {
        for(int i=0; i<maxs; ++i)
            a[i][i] = 1;
    }
};
int x, y;
int n;

Matrix mul(Matrix A, Matrix B)
{
    Matrix ret;
    for(int i = 0; i < maxs; ++i)
        for(int j = 0; j < maxs; ++j)
            for(int k = 0; k < maxs; ++k)
            {
                ret.a[i][j] += A.a[i][k]*B.a[k][j];
                ret.a[i][j] %= mod;
            }
    return ret;
}

Matrix qpow(Matrix A, int n)
{
    Matrix ret;
    ret.init();
    while(n)
    {
        if(n&1) ret = mul(ret, A);
        A = mul(A, A);
        n>>=1;
    }
    return ret;
}

int main()
{
    while(~scanf("%d %d", &x, &y))
    {
        scanf("%d", &n);
        Matrix A;
        A.a[0][0] = 1;
        A.a[0][1] = -1;
        A.a[1][0] = 1;
        A.a[1][1] = 0;
        A = qpow(A, n-1);
        int ans = A.a[1][0]*y + A.a[1][1]*x;
        ans %= mod;
        ans += mod;
        ans %= mod;
        printf("%d\n", ans);
    }
    return 0;
}