PrefixSumResolution

PrefixSum.java

import java.util.List;
import java.util.ArrayList;

public class Main
{
    public static int prefixSum(List<Integer> numbers, int head, int tail){
		List<Integer> factorialList = new ArrayList<>();
		Integer total = 0;
		for(Integer e : numbers){
		    total += e;
		    factorialList.add(total);
		}
		
		if(head > 0 && tail > 0) 
		    return factorialList.get(tail) - factorialList.get(head-1);
		
		return factorialList.get(head | tail);
    }
    
	public static void main(String[] args) {
		List<Integer> numbers = new ArrayList<>();
		numbers.add(1);
		numbers.add(2);
		numbers.add(3);
		numbers.add(4);
		numbers.add(5);
		
		//In order to work number list must be sorted!
		
		//[1 2 3 4 5]
		System.out.println(""+prefixSum(numbers,0,4));
		
		//[2 3 4 5]
		System.out.println(""+prefixSum(numbers,1,4));
		
		//[2 3 4]
		System.out.println(""+prefixSum(numbers,1,3));
	}
}