用java1+22+333++4444++55555+...+..++999999999=?

Question

如题所述

Answer 1

第一种

public class Main {

public static void main(String[] args) {

int n = 9; // 求和的最大数字

int sum = 0;

int num = 0;

for (int i = 1; i <= n; i++) {

num = num * 10 + i;

sum += num;

}

System.out.println("1+22+333+...+999999999 = " + sum);

}

}

第二种

---

public class Main {    public static void main(String[] args) {    

int n = 9; // 求和的最大数字

int sum = n*(n+1)/2 + (n-1)*n/2*111;

System.out.println("1+22+333+...+999999999 = " + sum);
}
}