Add the values of elements with the same index from two lists when the size of both the lists are different

Question

If first.size() is more than second.size() then the resultant list should be of the size of first else it should be the size of second.

import java.util.ArrayList;
import java.util.List;
import java.util.*;
import java.util.stream.Collectors;

public class Source {
    public static List<Integer> getSumOfListElements(List<Integer> first,List<Integer> second){
     if(first.size()>=second.size()){
        List<Integer> third = new ArrayList<Integer>();
        for (int i = 0; i < first.size(); i++) {
        third.add(first.get(i) + second.get(i));
        }
        return third;
     }else{
      List<Integer> third = new ArrayList<Integer>();
        for (int i = 0; i < second.size(); i++) {
        third.add(first.get(i) + second.get(i));
        }
        return third;
     }
    }

    public static void main(String[] args) {
       Scanner in = new Scanner(System.in);
       String str = in.nextLine();
       String str2 = in.nextLine();
       System.out.println(str);
       System.out.println(str2);
       List<Integer> list1 = Arrays.stream(str.split("\\s"))
        .mapToInt(Integer::parseInt)
        .boxed()
        .collect(Collectors.toList());
       List<Integer> list2 = Arrays.stream(str2.split("\\s"))
        .mapToInt(Integer::parseInt)
        .boxed()
        .collect(Collectors.toList());
       System.out.println(list1.size());
       System.out.println(list2.size());
       List<Integer> actual = Source.getSumOfListElements(list1,list2);
       System.out.println(actual);
    }
}

This is the code that I have written. It is giving exception Operation not permitted.

Answer 1

Your code does not work because when you try to add two numbers from lists (say first list size=20, and second list size=10), at one point i become larger than second list. When your for loop try to find element for that i , you will get an error.

To eradicate this, you should use a try catch block to bypass addition and add remaining elements of large list directly.

Take a look at the following code:

public static List<Integer> getSumOfListElements(List<Integer> first, List<Integer> second) {

        // declare 'third' list with size of max('first' list, 'second' list)
        List<Integer> third = new ArrayList<>(Math.max(first.size(), second.size()));

        // loop through max('first' list, 'second' list) number elements in both lists
        for (int i = 0; i < Math.max(first.size(), second.size()); i++) {
            try {
                third.add(first.get(i) + second.get(i));

                // at one point either first or second will be finished.
                // (say second is finished at this point)
                // then add remaining elements of first to third
            } catch (IndexOutOfBoundsException e) {
                if (first.size() > second.size()) third.add(first.get(i));
                else third.add(second.get(i));
            }
        }
        return third;
    }