CODEWITHSUNDEEP
javafor-looplinked-listnodes
user2923395
user2923395

Reputation: 327

Counting all the nodes in a Linked List

I'm trying to write a simple method to count all the nodes in the linked list. I know there are 7 items in the linked list, but it is returning just 6 of them.

Here is my method

public int count() {
    int count = 0;
    for (ListNode n = head; n.next != null; n = n.next) {
        count++;
    }
    return count;
}

And here is my ListNode.java

public class ListNode {

String name;        // a name in the list
ListNode next;      // the next node in the list
ListNode prev;      // the previous node in the list

/**
 * Constructor with just a name. This form would be most useful when
 * starting a list.
 */
public ListNode(String name) {
    this.name = name;
    next = null;
    prev = null;
}

/**
 * Constructor with a name and a reference to the previous list node. This
 * form would be most useful when adding to the end of a list.
 */
public ListNode(String name, ListNode node) {
    this.name = name;
    next = null;
    prev = node;
}
}

Upvotes: 1

Views: 15972

Answers (9)

Jesse Wijnakker
Jesse Wijnakker

Reputation: 1

You should check for null first. If not 0, then set 'counter = 1' before you loop through it. 

if (_first == null) return 0;
            int count = 1;
            for (ListNode n = _first; n.Next != null; n = n.Next)
            {
                count++;
            }
            return count;

Upvotes: 0

Mufanu
Mufanu

Reputation: 534

try this

public int count() {
    int count = 0;
    for (ListNode n = head; n != null; n = n.next) {
        count++;
    }
    return count;
}

Upvotes: 2

TheLostMind
TheLostMind

Reputation: 36304

n.next != null Is your problem. Change it to n!=null

 Example : 

List : 1--> 2 -->3--> 4-->null
Count :  1--> 2-->3-->here n=4 and n.next=null. So, your loop will break and count will be 3 (i.e; the last node will not be counted.)

Upvotes: 0

Rey Libutan
Rey Libutan

Reputation: 5314

The end node will fail n.next != null but it is part the the LinkedList, so you should consider that. It sounds like you simply have an indexing error.

Upvotes: 3

user2923395
user2923395

Reputation: 327

I figured it out.

for (ListNode n = head; n != null; n = n.next)

n.next !=null was the error.

Upvotes: 2

Josh Liptzin
Josh Liptzin

Reputation: 796

You aren't counting the last node. When you get to the last element to be counted, n.next will be null, and so count is never incremented. You might instead try a loop like the following:

ListNode n = head;
for (ListNode n = head; n != null; n = n.next) {
  count++;
}

Upvotes: 0

stinepike
stinepike

Reputation: 54682

public int count() {
    int count = 0;
    for (ListNode n = head; n != null; n = n.next) {
        count++;
    }
    return count;
}

Upvotes: 0

evanchooly
evanchooly

Reputation: 6233

You want to loop until n == null. As it stands, you're stopping one short.

Upvotes: 1

Tanuj Wadhwa
Tanuj Wadhwa

Reputation: 2045

Well that's because you are starting your count from 0, neglecting the first node.

Instead initialize count=1;

Upvotes: 0

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