The previous index and next index in an ArrayList can be obtained using the methods previousIndex() and nextIndex() respectively of the ListIterator interface. previousIndex() can also return -1 if it at the beginning of the list.
Example:
Input: list = [2, 3, 6, 8] listiterator is at the beginning find previous index. Output: -1 Input: list = [2, 3, 6, 8] listiterator is at the beginning find next index.
Steps to use previousIndex() and nextIndex():
- Create an empty ArrayList
- Add elements to ArrayList.
- Create a listiterator using listIterator() method.
Listiterator<Integer>iterator = arrList.listIterator();
- Now get the required index using the below commands
Syntax
iterator.previousIndex();
Returns: the index of the element that would be returned by a subsequent call to previous, or -1 if the list iterator is at the beginning of the list
Syntax
iterator.nextIndex();
Returns: the index of the element that would be returned by a subsequent call to next, or list size if the list iterator is at the end of the list
Example
Java
// Java program to get Previous and// next index using ListIteratorimport java.io.*;import java.util.ArrayList;import java.util.ListIterator;class PreviousAndNextIndex { public static void main(String[] args) { // create empty ArrayList ArrayList<Integer> arrList = new ArrayList<Integer>(); // add elements to the ArrayList arrList.add(5); arrList.add(10); arrList.add(15); arrList.add(20); arrList.add(25); arrList.add(30); // print the initial list System.out.println("Initial arraylist =>" + arrList); // initializing ListIterator ListIterator<Integer> iterator = arrList.listIterator(); // initially iterator is the beginning so // previousIndex() will return -1 System.out.println("previous index =>" + iterator.previousIndex()); // from -1 moving iterator to the 1st index iterator.next(); iterator.next(); // now iterator is at 1st index // so nextIterator() will return 2 System.out.println("Next index =>" + iterator.nextIndex()); }} |
Output:
Initial arraylist =>[5, 10, 15, 20, 25, 30] previous index =>-1 Next index =>2
Time Complexity: O(n)
Auxiliary Space: O(1)
As constant extra space is used.