Java Element-wise merge of two list

The key number here is 3: You want to loop 3 times. Each loop, you know what to do: Fetch the Xth number from input1, the Xth number from input2, put them together in a size-2 list, and that then forms the Xth entry in your output.

int[] in1 = ...; int[] in2 = ...; int[][] out; assert input1.length == input2.length; int len = input1.length; out = new int[len][]; for (int i = 0; i < len; i++) { out[i] = new int[] {input1[i], input2[i]}; } 

List<Integer> list1 = List.of(1,2,3); List<Integer> list2 = List.of(4,5,6); List<List<Integer>> merged = mergeLists(list1, list2); System.out.println(merged); 

Prints

[[1, 4], [2, 5], [3, 6]] 

This method accepts lists of any type <T> as long as they contain the same types and are the same length.

• throw an exception if different lengths.
• allocate a return ArrayList
• initialize an index to 0
• Using an enhanced for loop, iterate over one list and index the other
• add a new list via List.of() to the return list. Since List.of() is immutable it is passed as an argument to new ArrayList<>()
• return the result wnen the loop is finished.

public static <T> List<List<T>> mergeLists(List<T> list1, List<T> list2) { if (list1.size() != list2.size()) { throw new IllegalArgumentException("Lists must be the same size"); } List<List<T>> list = new ArrayList<>(); int i = 0; for (T v1 : list1) { list.add(new ArrayList<>(List.of(v1, list2.get(i++)))); } return list; } 

Ok I solved the problem like this:

public List<List<V>> Lister (List<V> list1, List<V> list2){ List<List<V>> result = new ArrayList<>(); if (list1.size() == list2.size()) { for(int i =0; i<list1.size(); i++){ List<V> tempList = new ArrayList<>(); tempList.add(list1.get(i)); tempList.add(list2.get(i)); result.add(tempList); } } return result; }