[Euler]Problem 34 - Digit factorials

一纯粹的paranoid

于 2013-04-16 22:10:00 发布

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分类专栏： Euler 文章标签： Euler

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本文探讨了一个数学问题，即找出所有等于其各位数阶乘之和的数，并计算它们的总和。通过编程实现，最终得到答案为40730。

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145 is a curious number, as 1! + 4! + 5! = 1 + 24 + 120 = 145.

Find the sum of all numbers which are equal to the sum of the factorial of their digits.

Note: as 1! = 1 and 2! = 2 are not sums they are not included.

临界点为 9! * 7 = 2540160

public class DigitFactorials {

	public static void main(String[] args) {
		long before = System.currentTimeMillis();

		new DigitFactorials().calculate();

		System.out.println("elapsed time is : " + (System.currentTimeMillis() - before));
	}

	private void calculate() {
		int number = 3;
		int sum = 0;
		int temp = 0;

		while (number <= 2540160) {
			int sumOfDigits = 0;
			temp = number;

			while (temp > 0) {
				sumOfDigits += calculateFactorial(temp % 10);
				temp = temp / 10;
			}

			if (sumOfDigits == number) {
				sum += sumOfDigits;
			}

			number++;
		}

		System.out.println("sum of all numbers is : " + sum);
	}

	private int calculateFactorial(int a) {

		if (a == 0) {
			return 1;
		}

		return a * calculateFactorial(a - 1);
	}

}

console :

sum of all numbers is : 40730
elapsed time is : 211