POJ 3744 Scout YYF I 矩阵快速幂

#include <stdio.h>
#include <algorithm>
#define REP(i, n) for(int i = 0; i < n; ++i)
#define FF(i, n) for(int i = 1; i <= n; ++i)
using namespace std;
const int O = 2;
int N;
struct Matrix{
    typedef double type;
    type mat[O][O];
    Matrix operator * (const Matrix &t) const{
        Matrix tmp;
        REP(i, N) REP(j, N){
            tmp.mat[i][j] = 0;
            REP(k, N){
                tmp.mat[i][j] = (tmp.mat[i][j] + mat[i][k] * t.mat[k][j]);
            }
        }
        return tmp;
    }
    Matrix operator + (const Matrix &t) const{
        Matrix tmp;
        REP(i, N) REP(j, N){
            tmp.mat[i][j] = (mat[i][j] + t.mat[i][j]);
        }
        return tmp;
    }
    Matrix operator - (const Matrix &t) const{
        Matrix tmp;
        REP(i, N) REP(j, N){
            tmp.mat[i][j] = (mat[i][j] - t.mat[i][j]);
        }
        return tmp;
    }
};
Matrix E, A;
Matrix pow(Matrix a, int k){
    Matrix res = E, tmp = a;
    while(k){
        if(k & 1) res = res * tmp;
        tmp = tmp * tmp;
        k >>= 1;
    }
    return res;
}
int work(){
    int n, mine[11], flag;
    double p, ans;
    N = O;
    mine[0] = 0;
    REP(i, N) REP(j, N) E.mat[i][j] = (i == j);
    while(~scanf("%d%lf", &n, &p)){
        FF(i, n) scanf("%d", &mine[i]);
        sort(mine + 1, mine + n + 1);
        flag = 0;
        FF(i, n){
            if(mine[i] - mine[i - 1] == 1) flag = 1;
        }
        if(mine[0] == 1 || flag){
            printf("%.7f\n", 0);
            continue;
        }
        A.mat[0][0] = p;
        A.mat[0][1] = 1;
        A.mat[1][0] = 1 - p;
        A.mat[1][1] = 0;
        ans = 1;
        FF(i, n){
            if(mine[i] == mine[i - 1]) continue;
            ans *= 1 - pow(A, mine[i] - mine[i - 1] - 1).mat[0][0];
        }
        printf("%.7f\n", ans);
    }
    return 0;
}
int main(){
    return work();
}