ProjectEuler第一题
Add all the natural numbers below one thousand that are multiples of 3 or 5.
求所有小于1000且能被3或5整除的自然数的和。

public class Task_1 {/** * 求所有小于1000且能被3或5整除的自然数的和。 * @param args */public static void main(String[] args) {System.out.println(sum1());System.out.println(sum2());}public static int sum1(){int n = 1000;int sum = 0;for(int i = 0;i < n;i++){if((i%3==0) || (i%5==0)){sum += i;}}return sum;}public static int sum2(){int n = 999;int s3,s5,s15;s3 = 3*((1+(n/3))*(n/3))/2;s5 = 5*((1+(n/5))*(n/5))/2;s15 = 15*((1+(n/15))*(n/15))/2;return s3+s5-s15;}}