The series: 1×2 2×3×4 ... n×(n 1)× ... ×2n

For example, if you enter 3, the output should be 386, because (1×2) (2×3×4) (3×4×5×6)=386.

I've tried various loops, but that is not even close to the desired result.

Though, I'll post it here:

int sum = 0, n = sc.nextInt();
for (int i = 1; i <= n; i  ) {
    sum = sum   i * (i   1); 
}

CodePudding user response：

I do not intent to resolve it for you, but you are missing that multiplication itself needs another loop for each of the number in the loop you created (from n to 2n).

I am giving you the solution, but hope you will try to understand it to realize where you missed it.

public class MyClass {
private static long calculateSeries(int n){
    long sum=0;
    for (int i = 1; i <= n; i  ) {

    // You are missing multiplication part in your logic.

        long mres=1;
        for (int j=i; j <= 2*i; j  ){
            mres=mres*j;
        }
    sum = sum   mres; 
    }
    return sum;
 }

public static void main(String args[]) {
  System.out.println(calculateSeries(3));
}
}

CodePudding user response：

I will do one better and give you advice on how to approach problems. Divide it into smaller problems :)

I wont give you the end result code, I think you wont learn much from it, but I will try to help you solve it learn from it.

So in words - given number N, sum the results of the multiplication of all the numbers between i to 2i for each 1<= i <= N.

So what you want to do:

1. receive input N
2. loop on all the numbers between 1 to N - you did everything until here, awesome :)
3. sum the results of the multiplication of all the numbers between i to 2i - this logic is incorrect in your code, I advise you to create a function that do this multiplication, just call and sum it in the loop from step #2