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;}