Java Program to Combine Two List by Alternatively Taking Elements
A list is an ordered sequence of elements stored together to form a collection. A list can contain duplicate as well as null entries. A list allows us to perform index-based operations, that is additions, deletions, manipulations, and positional access. Java provides an in-built interface <<java.util>> to perform list as well as other class-based functions.
Cases: There can occur two different scenarios while doing so as per the length of lists
- If list 2 gets exhausted while adding elements alternatively then the remaining elements of list 1 are the second list is remaining elements of list 1 to be added in the same sequence of occurrence.
- If list 1 gets exhausted and so on as discussed in the above case vice-versa
So, the Aim is to completely remove the elements from second one and add to first one list and whatever is left will be the second list.
Approach: The following approach is adopted to store elements alternatively in a merged list.
- Two lists are declared and initialized with a set of elements.
- Two counters, i and j are maintained to iterate over the length of the lists. The loop runs until the shorter length of both the lists.
- An empty list is maintained to store the merged contents of both the lists, in order of list1 followed by list2.
- At the end of the loop, one of the list, that is a shorter one is exhausted. A loop is then used to iterate over the remaining elements of the longer list and store them at the end one by one.
- The data type of the merged list should be similar to the individual lists.
Implementation: Two examples are discussed below considering both integer list and string lists
Example 1: String Lists
Java
// Java Program to Combine Two List// by Alternatingly Taking Elements// importing required packagesimport java.io.*;import java.util.*;import java.util.Iterator;// Class to access alternate elementsclass GFG { // Main driver method public static void main(String[] args) { // Creating(declaring) list1 List<String> list1 = new ArrayList<String>(); // Adding elements to list1 // Custom inputs list1.add("Geeks"); list1.add("Geeks"); list1.add("portal"); // Creating(declaring) list2 List<String> list2 = new ArrayList<String>(); // Adding elements to list2 // Custom inputs list2.add("for"); list2.add("is CSE"); list2.add("portal"); // Display message System.out.print("List1 contents: "); // Iterating over List1 Iterator iterator = list1.iterator(); // Condition check using hasNext() which holds true // till there is single element remaining in the // List while (iterator.hasNext()) { // Printing elements of List 1 System.out.print(iterator.next() + " "); } // Next Line System.out.println(); // Display message System.out.print("List2 contents: "); // Iterating over List 2 iterator = list2.iterator(); // Condition check using hasNext() which holds true // till there is single element remaining in the // List while (iterator.hasNext()) { // Printing elements of List 2 System.out.print(iterator.next() + " "); } // Declaring counters int i = 0; int j = 0; // Creating(declaring) merged List List<String> merged_list = new ArrayList<String>(); // Iterating over both the lists until // the elements of shorter List are exhausted while (i < list1.size() && j < list2.size()) { // Step 1: Adding List1 element merged_list.add(list1.get(i)); // Step 2: Adding List2 element merged_list.add(list2.get(j)); // Incrementing counters i++; j++; } // Iterating over the remaining part of List1 while (i < list1.size()) { merged_list.add(list1.get(i)); // Incrementing List1 counter i++; } // Iterating over the remaining part of List2 while (j < list2.size()) { merged_list.add(list2.get(j)); // Incrementing List1 counter j++; } // Next line System.out.println(); // Display message System.out.print("Merged List contents: "); // Iterators iterator = merged_list.iterator(); // Iterating over merged List using hasNext() method // which holds true till there is single element // remaining while (iterator.hasNext()) { // Printing merged list contents System.out.print(iterator.next() + " "); } }} |
Output
List1 contents: Geeks Geeks portal List2 contents: for is CSE portal Merged List contents: Geeks for Geeks is CSE portal portal
Example 2: Integer Lists
Java
// Java Program to Combine Two List// by Alternatingly Taking Elements// importing required packagesimport java.io.*;import java.util.*;import java.util.Iterator;// Classclass GFG { // Main driver method public static void main(String[] args) { // Creating(declaring) List1 List<Integer> list1 = new ArrayList<Integer>(); // Adding elements to List1 // Custom inputs list1.add(2); list1.add(4); list1.add(6); // Creating(declaring) List2 List<Integer> list2 = new ArrayList<Integer>(); // Adding elements to List2 // Custom inputs list2.add(1); list2.add(3); list2.add(5); list2.add(7); // Display message System.out.print("List1 contents: "); // Iterating over List1 Iterator iterator = list1.iterator(); // ConditionCheck using hasNext() method which hold // true till single element in remaining List while (iterator.hasNext()) { // Printing List1 contents System.out.print(iterator.next() + " "); } // New line System.out.println(); // Display message System.out.print("List2 contents: "); iterator = list2.iterator(); // ConditionCheck using hasNext() method which hold // true till single element in remaining List while (iterator.hasNext()) { // Printing List2 contents System.out.print(iterator.next() + " "); } // Setting counters to zeros int i = 0; int j = 0; // Creating(declaring) merged list List<Integer> merged_list = new ArrayList<Integer>(); // Iterating over both the lists // until the shorter list while (i < list1.size() && j < list2.size()) { // Step 1: Adding List2 element merged_list.add(list2.get(j)); // Step 2: Adding List1 element merged_list.add(list1.get(i)); // Incrementing counters i++; j++; } // Iterating over the remaining part of List1 // Case 1: Input: ShorterList following BiggerList while (i < list1.size()) { // Merge remaining List to List1, and // making List2 final as NULL List merged_list.add(list1.get(i)); i++; } // Case 2: Input: BiggerList following ShorterList while (j < list2.size()) { // Merge remaining List to List1,an d // making List2 -> NULL List merged_list.add(list2.get(j)); j++; } // New line System.out.println(); // Display message System.out.print("Merged List contents: "); // Iterating over merged list iterator = merged_list.iterator(); // Condition check using hasNext() method which // holds true till there is single element remaining // in the List while (iterator.hasNext()) { // Printing merged List contents i.e // FinalList = List1 + List2(Null final List) System.out.print(iterator.next() + " "); } }} |
Output
List1 contents: 2 4 6 List2 contents: 1 3 5 7 Merged List contents: 1 2 3 4 5 6 7
