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Java program to get the middle element of LinkedList in one iteration

　　Java Comprehensive Examples

In this example, we will learn how to get the middle element of a linked list in one iteration in Java.

To understand this example, make sure you first visit the following tutorials:

Java LinkedList Class

Example1Get the middle element of LinkedList by one iteration

Example

class LinkedList {
　　//Create an object of the Node class
　　//Represents the head of the list
　　Node head;
　　//Static inner class
　　static class Node {
　　　　int value;
　　　　//Connect each node to the next node
　　　　Node next;
　　　　Node(int d) {
　　　　　　value = d;
　　　　　　next = null;
　　　　}
　　}
　　public static void main(String[] args) {
　　　　//Create a LinkedList object
　　　　LinkedList linkedList = new LinkedList();
　　　　//Assign values to each linked list node
　　　　linkedList.head = new Node(1);
　　　　Node second = new Node(2);
　　　　Node third = new Node(3);
　　　　//Connect each node in the linked list to the next node
　　　　linkedList.head.next = second;
　　　　second.next = third;
　　　　//Print the linked list
　　　　Node pointer = linkedList.head;
　　　　System.out.print("LinkedList: ")
　　　　while (pointer != null) {
　　　　　　System.out.print(pointer.value　+　");
　　　　　　pointer = pointer.next;
　　　　}
　　　　//　Find the middle element
　　　　Node ptr1　= linkedList.head;
　　　　Node ptr2　= linkedList.head;
　　　　while (ptr1.next != null) {
　　　　　　//will point to the middle element1increase2，and ptr2increase1
　　　　　　//If ptr1will point to the last element
　　　　　　//ptr2will point to the middle element
　　　　　　ptr1　= ptr1.next;
　　　　　　if(ptr1.next != null) {
　　　　　　　　ptr1　= ptr1.next;
　　　　　　　　ptr2　= ptr2.next;
　　　　　　}
　　　　}
　　　　System.out.println("\nMiddle element: "　+　ptr2.value);
　　}
}

Output Result

LinkedList:　1　2　3　
Middle element:　2

In the above example, we have implemented the linked list data structure in Java. Then, we find the middle element of the linked list in a loop. Note the code,

　　　　while (ptr1.next != null) {
　　　　　　//will point to the middle element1increase2，and ptr2increase1
　　　　　　//If ptr1will point to the last element
　　　　　　//ptr2will point to the middle element
　　　　　　ptr1　= ptr1.next;
　　　　　　if(ptr1.next != null) {
　　　　　　　　ptr1　= ptr1.next;
　　　　　　　　ptr2　= ptr2.next;
　　　　　　}
　　　　}

Here, we have two variables ptr1and ptr2. We use these variables to traverse the linked list.

In each iteration, ptr1will access two nodes, while ptr2will access a single node in the linked list.

Now, when ptr1When reaching the end of the linked list, ptr2It is located in the middle. Therefore, we can obtain the middle position of the linked list in a single iteration.

Example2: Obtain the middle element of LinkedList using LinkedList class

Example

import java.util.LinkedList;
class Main {
　　public static void main(String[] args){
　　　　//Create a linked list using the LinkedList class
　　　　LinkedList<String> animals = new LinkedList<>();
　　　　//Add elements to LinkedList
　　　　animals.add("Dog");
　　　　animals.addFirst("Cat");
　　　　animals.addLast("Horse");
　　　　System.out.println("LinkedList:  ",　+　animals);
　　　　//Access the middle element
　　　　String middle = animals.get(animals.size())/2);
　　　　System.out.println("Middle Element:  ",　+　middle);
　　　　}
}

Output Result

LinkedList:  [Cat,  Dog,  Horse]
Middle Element:  Dog

In the above example, we used the LinkedList class to implement the linked list data structure. Note the expression

animals.get(animals.size())/2)

size()/ 2 - Return the position of the middle element
get() - Return the element located in the middle position

Java Comprehensive Examples

Java Serialization Java Ternary Operator