Counting all the nodes in a Linked List

问题

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;
}
}

回答1:

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.

回答2:

I figured it out.

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

n.next !=null was the error.

回答3:

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

回答4:

try this

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

回答5:

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

Instead initialize count=1;

回答6:

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

回答7:

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++;
}

回答8:

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.)

回答9:

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;

来源：https://stackoverflow.com/questions/22086128/counting-all-the-nodes-in-a-linked-list

标签

java

for-loop

linked-list

nodes