[CF1177B]Digits Sequence (Hard Edition)题解

一个简单的模拟，首先先计算当前是几位数，然后根据几位数推断当前的数是什么，然后求出该位即可

#include <cstdio>

int main(){
    long long k; scanf("%lld", &k);
    long long cur = 1, cnt = 9;
    while (cur * cnt < k){k -= cur * cnt; cnt *= 10, ++cur;}
    long long mod = k % cur, a = (k - 1) / cur;
    if (!mod) mod = cur;
    long long num = 1;
    for (int i = 1; i < cur; ++i) num *= 10;
    num += a;
    for (int i = 1; i <= (cur - mod); ++i) num /= 10;
    printf("%lld", num % 10);
    return 0;
}