O(1)得到螺旋矩阵的值

LL ind(LL x, LL y, LL n){
    LL qs = n / , q = min(n - y + , min(n - x + , min(x, y))) - ;
    if (x == qs +  && y == qs + )    return n * n;
    LL ans = 1ll * q * ( * qs +  * (qs - q + )) / ;
    if (n - x == q)    ans += n - q - y + ;
    else if (y -  == q)    ans += n -  * q +  + n - q -  - x;
    else if (x -  == q)    ans += n -  * q +  + n -  * q -  + y - q - ;
    else ans += n -  * q +  + n -  * q -  + n -  * q -  + x - q - ;
    return ans;
}

解析：https://blog.csdn.net/weixin_42165981/article/details/100187841