(Problem 40)Champernowne's constant

An irrational decimal fraction is created by concatenating the positive integers:

0.123456789101112131415161718192021...

It can be seen that the 12^th digit of the fractional part is 1.

If d_n represents the n^th digit of the fractional part, find the value of the following expression.

d₁  d₁₀  d₁₀₀  d₁₀₀₀  d₁₀₀₀₀  d₁₀₀₀₀₀  d_1000000

#include <stdio.h>



int solve()

{

    int i, k, result, n, t, temp;

    int s[8], a[101];

    i = k = 0;

    n = result = 1;

    t = 0;

    while(1) {

        temp = n;

        i = 0;

        while(temp) {

            s[i++] = temp % 10;

            temp /= 10;

        }

        i--;

        while(i >= 0) {

            a[k] = s[i];

            t++;

            if(t == 1 || t == 10 || t == 100 || t == 1000 || t == 10000 || t == 100000 || t == 1000000) {

                result *= a[k];

                if(t == 1000000)  return result;

            }

            if(k == 100) {

                k = 1;

            } else {

                k++;

            }

            i--;

        }

        n++;

    }

}



int main(void)

{

    printf("%d\n",solve());

    return 0;

}

 

Answer:

210