problem040.cpp

#include <cmath>
#include <iostream>

int champernowneNthDigit(int n)
{
 int digits = 0;
 int upperVal = 1;
 int upperIndex = 0;
 do {
 ++digits;
 upperIndex += 9 * upperVal * digits;
 upperVal *= 10;
 } while (n > upperIndex);
 int dist = upperIndex - n;
 int val = upperVal - dist / digits - 1;
 int div = pow(10, dist % digits);
 return val / div % 10;
}

int main()
{
 int ans = 1;
 int n = 1;
 for (int i = 0; i < 7; ++i) {
 ans *= champernowneNthDigit(n);
 n *= 10;
 }
 std::cout << "Answer: " << ans << '\n';
 return 0;
}