计算1->n中数字x出现的次数

LL Count(LL n,LL x) {    LL cnt=0,k;    for (LL i=1;k=n/i;i*=10)     {        int high=k/10;        if (x==0)         {            if (high) high--;            else break;        }        cnt+=high * i;        LL cur = k % 10;        if (cur>x)cnt+=i;        else if (cur==x) cnt+=n-k*i+1;    }    return cnt;}