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???????????????????????????????????????? $A$ ? $n$ ??????? $A^n = A \cdot A \cdot \ldots \cdot A$?? $n$ ? $A$??????????? $O(n)$ ??????????????????????????????????????? $O(\log n)$??????????

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#include 
   
    using namespace std;#define mod(x) ((x) % m)int k, m;struct mat {    int d[10][10];    mat operator*(const mat x) {        mat ret;        int tmp;        for (int i = 0; i < 10; i++) {            for (int j = 0; j < 10; j++) {                tmp = 0;                for (int k = 0; k < 10; k++) {                    tmp = mod(tmp + d[i][k] * x.d[k][j]);                }                ret.d[i][j] = tmp;            }        }        return ret;    }    void init_unit() {        for (int i = 0; i < 10; i++)            for (int j = 0; j < 10; j++)                d[i][j] = (i == j) ? 1 : 0;    }    void init() {        for (int i = 0; i < 10; i++)            for (int j = 0; j < 10; j++)                d[i][j] = (i == j + 1) ? 1 : 0;    }    void set(int i, int v) {        d[9 - i][9] = v;    }};mat fastPow(mat base, int pow) {    mat res;    res.init_unit();    while (pow) {        if (pow & 1)            res = res * base;        base = base * base;        pow >>= 1;    }    return res;}int main() {    int tmp;    while (scanf("%d%d", &k, &m) == 2) {        if (k < 10) {            printf("%d\n", k % m);            continue;        }        a.init();        for (int i = 0; i < 10; i++)            scanf("%d", &tmp), a.set(i, tmp);        a = fastPow(a, k - 9);        int ans = 0;        for (int i = 0; i < 10; i++)            ans = mod(ans + a.d[i][9] * i);        printf("%d\n", ans);    }    return 0;}
   

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