规律题

#include 
      
       using namespace std;long long        mi[20], len[50], eachlen[50];long long    make(long long num, long long n){    long long        i, x, goal;    i = 1;    while (true)    {        if (n > i * (mi[i] - mi[i - 1]))            n -= i * (mi[i] - mi[i - 1]);        else            break;        i++;    }    x = n / i;    if (n % i == 0)        x -= 1;    n -= x * i;    goal = x + mi[i - 1];    n = i - n + 1;    for (i = 0; i < n - 1; i++)        goal /= 10;    return goal % 10;}long long    work(long long n){    long long        i, start, each, l, r, mid, num;        i = 0;    while (n > len[i])        i++;    i--;    start = i;    n -= len[i];    each = eachlen[i];    l = 0;    r = mi[start + 1] - mi[start];    while (l < r)    {        mid = (l + r) / 2;        if ((l + r) % 2 != 0)            mid +=1;        if ((each + start + 1 + each + mid * (start + 1)) * mid / 2 < n)            l = mid;        else            r = mid - 1;    }    mid = l;    n -= (each + start + 1 + each + mid * (start + 1)) * mid / 2;    num = mi[start] + mid;    return make(num, n);}int main(){    long long        i, t, n;    //freopen("t.txt", "r", stdin);    mi[0] = 1;    for (i = 1; i <= 5; i++)        mi[i] = mi[i - 1] * 10;    memset(len, 0, sizeof(len));    memset(eachlen, 0, sizeof(eachlen));    for (i = 1; i <= 5; i++)    {        len[i] = len[i - 1];        len[i] += eachlen[i - 1] * (mi[i] - mi[i - 1]);        len[i] += (i + i * (mi[i] - mi[i - 1])) * (mi[i] - mi[i - 1]) / 2;        eachlen[i] += eachlen[i - 1];        eachlen[i] += i * (mi[i] - mi[i - 1]);    }    cin >> t;    while (t--)    {        cin >> n;        cout << work(n) << endl;    }    return 0;}