Solution to Project Euler Problem 40: Champernowne's constant - An irrational decimal fraction is created by concatenating the positive integers: 0.123456789101112131415161718192021... It can be seen that the 12th digit of the fractional part is 1. If dn represents the nth digit of the fractional part, find the value of the following expression. d1 × d10 × d100 × d1000 × d10000 × d100000 × d1000000

• Java Code

package sikademy;
/**
 *
 * @author Archangel Macsika
 * Copyright (c) Sikademy. All rights reserved
 */

public class SikademyEulerSolution {
	
	public String run() {
		StringBuilder sb = new StringBuilder();
		for (int i = 1; i < 1000000; i++)
			sb.append(i);
		
		int prod = 1;
		for (int i = 0; i <= 6; i++)
			prod *= sb.charAt(pow(10, i) - 1) - '0';
		return Integer.toString(prod);
	}

        public static int pow(int x, int y) {
		if (x < 0)
			throw new IllegalArgumentException("Negative base not supported");
		if (y < 0)
			throw new IllegalArgumentException("Negative exponent");
		int z = 1;
		for (int i = 0; i < y; i++) {
			if (Integer.MAX_VALUE / z < x)
				throw new ArithmeticException("Overflow");
			z *= x;
		}
		return z;
	}

	public static void main(String[] args) {
                SikademyEulerSolution solution = new SikademyEulerSolution();
		System.out.println(solution.run());
	}	
}

• Python Code

# 
# @author Archangel Macsika
# Copyright (c) Sikademy. All rights reserved.
# 


def compute():
	s = "".join(str(i) for i in range(1, 1000000))
	ans = 1
	for i in range(7):
		ans *= int(s[10**i - 1])
	return str(ans)


if __name__ == "__main__":
	print(compute())