当两个列表的大小不同时，将两个列表中具有相同索引的元素的值相加

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;
    }