Nth Digit LeetCode solution in C++

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class Solution {
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 public:
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#define ll long long
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  int findNthDigit(int n) {
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    if (n <= 9) return n;
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    ll i = 1;
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    ll sum = 0;
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    while (true) {
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      ll a = (9 * pow(10, i - 1)) * i;
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      if (n - a < 0) {
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        break;
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      } else {
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        sum += 9 * pow(10, i - 1);
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        n -= a;
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      }
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      i++;
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    }
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    ll x = 0;
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    ll mod = n % i;
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    n = (n / i);
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    n += sum;
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    if (mod == 0)
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      return n % 10;
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    else {
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      n++;
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      ll x = i - mod;
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      while (x--) {
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        n /= 10;
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      }
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    }
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    return n % 10;
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  }
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};