Problem 3

问题描述：
The prime factors of 13195 are 5, 7, 13 and 29.

What is the largest prime factor of the number 600851475143 ?


找出一个数字的最大因子。

public static boolean IsPrime(long number) {
		int begin = 2;
		int end = (int) Math.sqrt(number) + 1;
		for (int i = begin; i < end; i++) {
			if (number % i == 0)
				return false;
		}
		return true;
	}

	public long FindLargestPrime1(long number) {

		long largest_prime = 1;
		int middle = (int) Math.sqrt(number);
		System.out.println(middle);
		for (int i = middle; i > 1; i--) {
			if (IsPrime(i) && number % i == 0) {
				if (i > largest_prime) {
					largest_prime = i;
				}
				do {
					number = number / i;
				} while (number % i == 0);
			}
		}
		if(IsPrime(number)&&number!=1){
			largest_prime = number;
		}
		return largest_prime;
	}

这个还是有点复杂！

可以改进！
完全可以从2,3...除起来
每次记录下当前的除数就好了~