斐波那契数列——矩阵快速幂解法

#include <iostream>
#include <algorithm>
using namespace std;
 
typedef long long ll;
const ll mod = 1000000007;
 
struct Matrix {
    ll num[2][2];
    void initial() {
        num[0][0] = num[0][1] = num[1][0] = num[1][1] = 0;
    }
};
 
Matrix Multiply(Matrix A, Matrix B) {
    Matrix C;
    C.initial();
    C.num[0][0] = ((A.num[0][0] * B.num[0][0]) % mod + (A.num[0][1] * B.num[1][0]) % mod) % mod;
    C.num[0][1] = ((A.num[0][0] * B.num[0][1]) % mod + (A.num[0][1] * B.num[1][1]) % mod) % mod;
    C.num[1][0] = ((A.num[1][0] * B.num[0][0]) % mod + (A.num[1][1] * B.num[1][0]) % mod) % mod;
    C.num[1][1] = ((A.num[1][0] * B.num[0][1]) % mod + (A.num[1][1] * B.num[1][1]) % mod) % mod;
    return C;
}
 
Matrix MatrixPower(Matrix m, ll p){
    Matrix res;
    res.initial();
    res.num[0][0] = res.num[1][1] = 1;
    for ( ; p != 0; p >>= 1){
        if (p & 1){
            res = Multiply(res, m);
        }
        m = Multiply(m, m);
    }
    return res;
}
 
int main () {
    ll x, y, p;
    Matrix A;
    Matrix B;
    Matrix ans;
    A.initial(); B.initial(); ans.initial();
    cin >> x >> y >> p;
    x %= mod;  y %= mod;    //非常重要，我就是在这里WA,WA,WA的
    if (p == 1) {
        cout << x << endl;
        return 0;
    }
    A.num[0][0] = 1; A.num[0][1] = 1; A.num[1][0] = 1; A.num[1][1] = 0;
    B.num[0][0] = y; B.num[0][1] = x; B.num[1][0] = x; B.num[1][1] = 0;
    ans = MatrixPower(A, p - 2);
    ans = Multiply(ans, B);
    cout << ans.num[0][0] << endl;
    
    return 0;
}