题目：

题解：

const mod int = 1e9 + 7

type matrix [6][6]int

func (a matrix) mul(b matrix) matrix {
    c := matrix{}
    for i, row := range a {
        for j := range b[0] {
            for k, v := range row {
                c[i][j] = (c[i][j] + v*b[k][j]) % mod
            }
        }
    }
    return c
}

func (a matrix) pow(n int) matrix {
    res := matrix{}
    for i := range res {
        res[i][i] = 1
    }
    for ; n > 0; n >>= 1 {
        if n&1 > 0 {
            res = res.mul(a)
        }
        a = a.mul(a)
    }
    return res
}

func checkRecord(n int) (ans int) {
    m := matrix{
        {1, 1, 0, 1, 0, 0},
        {1, 0, 1, 1, 0, 0},
        {1, 0, 0, 1, 0, 0},
        {0, 0, 0, 1, 1, 0},
        {0, 0, 0, 1, 0, 1},
        {0, 0, 0, 1, 0, 0},
    }
    res := m.pow(n)
    for _, v := range res[0] {
        ans = (ans + v) % mod
    }
    return ans
}