Merging Two ArrayList

Question

Write a method

public static ArrayList merge(ArrayList a, ArrayList b)

that merges two array lists, alternating elements from both array lists. If one array list is shorter than the other, then alternate as long as you can and then append the remaining elemts from the longer array list. For example, if a is

1 4 9 16

and b is

9 7 4 9 11

then merge returns the array list

1 9 4 7 9 4 16 9 11

Okay this is my code so far.

All I need to do is merged two inputs given by user in same fashion as here

I asked same question earlier but that was for Array and i got satisfied result.

I tried solutions from that link but I have no result If someone can please give me quick hint on how to merge two ArrayList, I will appreciate the help.

import java.util.ArrayList;
import java.util.Scanner;


public class HomeWork6_27_B{


public static void main(String arg[]) {

    Scanner scan = new Scanner(System.in);
    Scanner scan2 = new Scanner(System.in);
    ArrayList<Integer> a = new ArrayList<>();
    ArrayList<Integer> b = new ArrayList<>();

    System.out.print("Enter Array of numbers in First Set, type 0 when finished:");
    System.out.println();
    int in = scan.nextInt();
    a.add(in);
    in = scan.nextInt();
    while (in !=0){
        a.add(in);
        in = scan.nextInt();
    }
    System.out.println("End of First Set");

    System.out.print("Enter Array of numbers in Second Set, type 0 when finished:");
    System.out.println();
    int in2 = scan2.nextInt();
    b.add(in2);
    in2 = scan2.nextInt();
    while (in2 !=0){
        b.add(in2);
        in2 = scan2.nextInt();
    }
    System.out.println("End of Second Set");
}

}

timleathart · Accepted Answer · 2015-02-26 03:14:54Z

1

I haven't used java for a while but I'm pretty sure this should work. Basically we loop to the end of the longer list, and add an element from each input list if we haven't reached the end of that input list.

ArrayList<Integer> merged = new ArrayList<Integer>();

// Merge the lists
for (int i = 0; i < Math.max(a.size(), b.size()); i++) {
    if (i < a.size()) merged.add(a.get(i));
    if (i < b.size()) merged.add(b.get(i));
}

for (int i = 0; i < merged.size(); i++) {
    System.out.print(merged.get(i).toString() + " ");
}

edited Feb 26, 2015 at 3:14

answered Feb 26, 2015 at 3:05

timleathart

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11 Comments

BabyC0d3eR Over a year ago

so my out put would be system.out.println(merged)?

BabyC0d3eR Over a year ago

I appreciate help but I am really new to java. I am not and not sure how to implement that into my code.

Shashank Over a year ago

Pretty perfect answer for someone who hasn't used Java in a while. +1.

timleathart Over a year ago

I have edited the original post. You need to loop through the new list and print each element separately.

Shashank Over a year ago

@TimLeathart make sure to print out the element at index i, not the int i itself. Also due to autoboxing and unboxing and some other stuff in Java, there's no need to use .toString(). It can even understand what to do with string concatenation.

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