We are going to find lenght of a Linked List using iterative method. You can read the recursive method here.
The simple logic to find length of a Linked list is – to increment a counter until you run out of nodes.
Here is the simple algorithm.
Step 1 :- Initialize a counter to 0
Step 2 :- Until we run out of nodes i.e our reference to the nodes become null.
2-a) increment the counter by 1
2-b) move to the next node
Step 3 :- return the value of counter
I am providing two implementations.
One is going to be verbose, and other one will be more concise and readable.
Implementation 1 :-
private static int length(Node head) {
if(head == null) return 0;
int length = 0;
while(head != null) {
++length;
head = head .next;
}
return length;
}
You can see that we have initialized a variable and we are incrementing it until we run out of nodes.
Implementation 2 :-
private static int lengthBetter(Node head) {
int length = 0;
while(head != null) {
++length;
head = head .next;
}
return length;
}
This one is more concise. It does not have the if-statement.
Now, I am going to walk you through the code.
The Step 1 :- create a counter
int length = 0;
The Step 2 :- while we have nodes – 1. increment counter 2. move to the next node
while(head != null) {
++length;
head = head .next;
}
The step 3 :- return the counter value
return length;
Complete Code
public class LinkedListLengthIterative {
private static class Node {
int data;
Node next;
Node prev;
Node(final int data) {
this .data = data;
}
}
public static void main(String ... args) {
Node a = new Node(1);
Node b = new Node(2);
Node c = new Node(3);
Node d = new Node(4);
a .next = b;
b .next = c;
c .next = d;
System.out.println("Length is :- " + length(a));
System .out .println("Length is :- " + lengthBetter(a));
}
//Method 1
private static int length(Node head) {
if(head == null) return 0;
int length = 0;
while(head != null) {
++length;
head = head .next;
}
return length;
}
//Method 2
private static int lengthBetter(Node head) {
int length = 0;
while(head != null) {
++length;
head = head .next;
}
return length;
}
}