UVA 10689 Yet another Number Sequence

题意：斐波那契给前两项，求出第n项，并保留m位

思路：挺裸的矩阵快速幂，就是取模的值是10^m

#include <cstdio>  
#include <cstring>  
  
const int mod[5] = {0, 10, 100, 1000, 10000};  
int t, a, b, n, m;  
  
struct mat {  
    int v[2][2];  
    mat() {memset(v, 0, sizeof(v));}  
    mat operator * (mat c) {  
        mat ans;  
        for (int i = 0; i < 2; i++) {  
            for (int j = 0; j < 2; j++) {  
                for (int k = 0; k < 2; k++) {  
                    ans.v[i][j] = (ans.v[i][j] + v[i][k] * c.v[k][j]) % mod[m];  
                }  
            }  
        }  
        return ans;  
    }  
};  
  
mat pow_mod(mat x, int k) {  
    mat ans;  
    ans.v[0][0] = ans.v[1][1] = 1;  
    while (k) {  
        if (k&1) ans = ans * x;  
        x = x * x;  
        k >>= 1;  
    }  
    return ans;  
}  
  
int solve() {  
    if (n == 0) return a;  
    if (n == 1) return b;  
    mat ans;  
    ans.v[0][0] = ans.v[0][1] = ans.v[1][0] = 1;  
    ans = pow_mod(ans, n - 1);  
    return (ans.v[0][0] * b + ans.v[0][1] * a);  
}  
  
int main() {  
    scanf("%d", &t);  
    while (t--) {  
        scanf("%d%d%d%d", &a, &b, &n, &m);  
        printf("%d\n", solve() % mod[m]);  
    }  
    return 0;  
}