【HNOI2011】数学作业

分段矩乘即可

# include <stdio.h>
# include <stdlib.h>
# include <iostream>
# include <string.h>
# define ll long long
# define RG register
# define IL inline
# define UN unsigned
# define mem(a, b) memset(a, b, sizeof(a))
# define min(a, b) ((a) < (b)) ? (a) : (b)
# define max(a, b) ((a) > (b)) ? (a) : (b)
using namespace std;

ll m;

struct Matrix{
    ll a[3][3];
    IL void Clear(){mem(a, 0);}
    IL void First(){a[0][0] = a[1][1] = a[2][2] = 1;}
    IL Matrix operator *(Matrix &B){
        RG Matrix C; C.Clear();
        for(RG int i = 0; i < 3; i++)
            for(RG int j = 0; j < 3; j++)
                for(RG int k = 0; k < 3; k++){
                    C.a[i][j] += (a[i][k] * B.a[k][j]) % m;
                    C.a[i][j] %= m;
                }
        return C;
    }
} S, T[19];

IL ll Get(){
    RG char c = '!'; RG ll z = 1, num = 0;
    while(c != '-' && (c < '0' || c > '9'))
        c = getchar();
    if(c == '-')
        z = -1, c = getchar();
    while(c >= '0' && c <= '9')
        num = num * 10 + c - '0', c = getchar();
    return num * z;
}

IL void Pow(RG ll n, RG int x){
    while(n){
        if(n & 1) T[x] = T[x] * S;
        S = S * S;
        n >>= 1;
    }
}

int main(){
    RG ll n = Get();
    RG UN ll t = n;
    m = Get();
    RG int k = 0;
    while(t) t /= 10, k++;
    t = 1;
    for(RG int i = 1; i < k; i++){
        S.Clear();
        t *= 10; S.a[0][0] = t % m; T[i].First();
        S.a[1][0] = S.a[1][1] = S.a[2][0] = S.a[2][1] = S.a[2][2] = 1;
        Pow(t - t / 10, i);
    }
    S.Clear();
    t *= 10; S.a[0][0] = t % m; T[k].First();
    S.a[1][0] = S.a[1][1] = S.a[2][0] = S.a[2][1] = S.a[2][2] = 1;
    Pow(n - t / 10 + 1, k);
    S.Clear(); S.First();
    for(RG int i = 1; i <= k; i++)
        S = S * T[i];
    printf("%d\n", S.a[2][0] % m);
    return 0;
}