/* package whatever; // don't place package name! */
 
import java.util.*;
import java.lang.*;
import java.io.*;
 
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		int[] arr = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
            int l = 3; int r =7;
            int[] arr1 = new int[arr.length];
            int c=0;
            for(int i =0; i< arr.length; i++){
                arr1[i] = c+arr[i];
                c+= arr[i];
            }
            if(l ==0 ){System.out.println("ans -->"+(arr1[r]));}
            else
            {System.out.println("ans -->"+(arr1[r]-arr1[l-1]));}
	}
}

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