I'm trying to delete a node in the linked list and when I performed this code, it removes all the nodes which are before the index I gave. Is there a way that I can correct it?
public void DeleteAt(int index)
{
if (index == 0)
{
head = head.next;
}
else
{
Node a = head;
Node n1 = null;
for(int i=0; i<index-1; i++)
{
n1 = a.next;
a.next = n1.next;
}
}
}
Your loop is removing a node in each iteration. You should only do this once, after the loop.
Secondly, you should protect your code against dereferencing NULL values.
NB: ...and use variable names that are descriptive. a and n1 are cryptic; that does not help anyone that tries to understand your code. i is an exception, as it is common to name an integer loop variable like that.
public void DeleteAt(int index)
{
if (head == NULL) // List is empty; nothing to do
{
return;
}
if (index == 0)
{
head = head.next;
}
else
{
Node node = head;
for(int i=0; i<index-1; i++)
{
node = node.next;
if (node == NULL) { // Index is out of range
return;
}
}
if (node.next != NULL) { // Index is not out of range
node.next = node.next.next;
}
}
}
Related
I faced a very weird problem. I can`t insert a node by index into a custom linked list. So here it is my method:
public void Insert(int index, T item)
{
if(item == null)
throw new ArgumentNullException(nameof(item), "Item is equal null.");
if (index > Count || index < 0)
throw new ArgumentOutOfRangeException(nameof(index),"Index out of range.");
Item<T> newNode = new Item<T>(item);
Item<T> currentItem = Head;
if (index == 0)
{
newNode.Next = Head;
return;
}
var x = FindItemByData(this[index]);
while (currentItem.Next != null)
{
if (currentItem.Next == x)
{
currentItem.Next = newNode;
newNode.Next = FindItemByData(this[index]);
}
currentItem = currentItem.Next;
}
}
And there are Item class:
public class Item<T>
{
public T Data { get; set; }
public Item<T> Next { get; set; }
public Item(T data)
{
Data = data;
Next = null;
}
}
Indexator of my linked list returns a data from specify node in the list, so I need to insert a new node to list with data: item. For example: I have a list of items ⛑ 🧶 🦚 🧥. And I need to insert on index 1 - element 🦋, result list might be ⛑ 🦋 🧶 🦚 🧥.
I tried to show that this problem doesn't simple because I can`t found a solution for insertion by index, there are always only 'Insert before'.
The method that I implemented doesn't work. Hopefully, someone can help me with this.
Also, there the test to this method:
[TestCase(0)]
[TestCase(5)]
[TestCase(2)]
public void Insert_AtPositionValue_ReturnCount(int position)
{
//arrange
CustomList<int> list = new CustomList<int>(1, 2, 7, 8, 10);
//act
int elementToInsert = 100;
list.Insert(position, elementToInsert);
int count = list.Count;
int actualValue = list[position];
//arrange
Assert.Multiple(() =>
{
Assert.AreEqual(elementToInsert, actualValue, message: "Insert or Get Count work incorrectly ");
Assert.AreEqual(6, count, message: "Insert or Get Count work incorrectly ");
});
}
I think you are iterating the list two times, one with FindItemByData and one to recatch the item in the while.
You also forgot to append the rest of the list to the new node.
public void Insert(int index, T item)
{
if(item == null)
throw new ArgumentNullException(nameof(item), "Item is equal null.");
if (index > Count || index < 0)
throw new ArgumentOutOfRangeException(nameof(index),"Index out of range.");
Item<T> newNode = new Item<T>(item);
Item<T> currentItem = Head;
if (index == 0)
{
newNode.Next = Head;
Head = newNode; //you forgot this. You have to reset the head of the list.
return;
}
//delete this <var x = FindItemByData(this[index]);>
for (int i = 0; i<index-1; i++) //if index == 1 I want to add right after head
{
currentItem = currentItem.Next;
}
newNode.Next = currentItem.Next; //append the rest of the list after newNode
currentNode.Next = newNode; //insert new node after the current node
}
Actually the previous author was close. But the error was in passing links to the next element.
public void Insert(int index, T item)
{
if (item == null)
throw new ArgumentNullException(nameof(item), "Item is equal null.");
if (index > Count || index < 0)
throw new ArgumentOutOfRangeException(nameof(index), "Index out of range.");
Item<T> newNode = new Item<T>(item);
Item<T> currentItem = Head;
if (index == 0)
{
newNode.Next = Head;
Head = newNode;
Count++;
return;
}
for (int i = 0; i < index - 1; i++)
{
currentItem = currentItem.Next;
}
newNode.Next = currentItem;
currentItem.Next = newNode;
Count++;
}
I made big research in this forum and found many "solutions" but none of them work.
Maybe my situation is a little bit different and I maybe someone can see where is the problem. I need to delete each Node element which is has "value" less than given(kruvis).
public void Delete()
{
if (Start == null) return;
if (Start.Next == null)
{
Start = null;
return;
}
if (Current.Next == null)
{
Current = null;
}
Node temp = Start;
while (temp.Next.Next != null)
{
if (temp.Next == Current)
{
temp.Next = Current.Next;
Current = temp;
return;
}
temp = temp.Next;
}
}
There is another function(loop in function) in diferent class
for (MenesioAgentai.Pradzia(); MenesioAgentai.ArYra(); MenesioAgentai.Sekantis())
{
if (MenesioAgentai.GautiT().Kruvis <= kruvis)
{
kruvioSuma += MenesioAgentai.GautiT().Kruvis;
PasalintiAgentoPrenumeratorius(pren, MenesioAgentai.GautiT());
MenesioAgentai.Delete();
}
}
The problem is that the first and last element is not deleted
in NodeList class I have 3 nodes Start, End, Current. (and sealed class Node with T data and Node Next)
Deleting node from a linked list is a bit tricky when the head node also needs to be deleted. An easier way is to add a sentinel node at the beginning. The following Java code explains how to delete nodes that have a smaller value than a given value. I used a value of type int for simplicity.
/*
// Node definition
class Node {
Node next;
int val;
Node(int val) {
this.val = val;
}
}
*/
public Node delete(Node head, int k) {
Node sentinel = new Node(Integer.MIN_VALUE);
sentinel.next = head;
Node prev = sentinel, curr = sentinel.next;
while(curr != null) {
while(curr != null && curr.val < k) {
curr = curr.next;
}
prev.next = curr;
prev = curr;
if(curr != null) {
curr = curr.next;
}
}
return sentinel.next;
}
I've implemented Singly linked list using C# . Can anyone please look into the following code and suggest where I'm wrong?
public int RemoveLast()
{
if (Head != null)
{
var curNode = Head;
while (curNode.Next != null)
{
curNode = curNode.Next;
}
var lastNodeValue = curNode.Value;
curNode = null;
Size--;
return lastNodeValue;
}
return -1;
}
This function does not remove the last node. I'm unable to figure out what's wrong. When while loop ends, we have the reference of node in curNode whose next is null. It means this is the last node. At the end, I'm setting this node to null. But when I use Display function. It displays the last node as well. This is not deleting the last node.
Here is my display function:
public string Display()
{
if (Head == null)
{
return string.Empty;
}
var curNode = Head;
var builder = new StringBuilder();
while (curNode.Next != null)
{
builder.Append($"{curNode.Value} ");
curNode = curNode.Next;
}
builder.Append($"{curNode.Value} ");
return builder.ToString();
}
You need to go to the last-but-one node, and change its Next to null:
public int RemoveLast()
{
if (Head != null)
{
var curNode = Head;
while (curNode.Next?.Next != null)
{
curNode = curNode.Next;
}
var lastNodeValue = curNode.Next?.Value ?? -1;
curNode.Next = null;
Size--;
return lastNodeValue;
}
return -1;
}
Note that if you also want Head to be set to null if its the only node, then you can do that like so:
public int RemoveLast()
{
if (Head != null)
{
var curNode = Head;
while (curNode.Next?.Next != null)
{
curNode = curNode.Next;
}
int lastNodeValue;
if (Head.Next == null)
{
lastNodeValue = Head.Value;
Head = null;
}
else
{
lastNodeValue = curNode.Next?.Value ?? -1;
}
curNode.Next = null;
Size--;
return lastNodeValue;
}
return -1;
}
I have to say though, this Head property looks a bit dubious - it should perhaps belong to a different class.
[x] -> [x] -> [x] -> null
^
curNode (becomes null)
^
this reference still exists
When doing curNode = null you do not change any reference in the list. curNode variable is changed only, it is pointing to the last element before operation and becomes null afterwards.
Try always keep reference to the node before last:
public int RemoveLast()
{
if (Head != null)
{
var curNode = Head;
// Corner case when there is only one node in the list
if (Head.Next == null)
{
Head = null;
Size--;
return curNode.value;
}
var beforeLastNode = curNode;
curNode = curNode.Next;
while (curNode.Next != null)
{
beforeLastNode = curNode;
curNode = curNode.Next;
}
var lastNodeValue = curNode.Value;
beforeLastNode.Next = null;
Size--;
return lastNodeValue;
}
return -1;
}
You need to make the curNode.Next value null on the previous node.
'curNode' is a local variable, setting it null doesn't do anything except maybe extend its GC life.
public int RemoveLast()
{
if (Head != null)
{
var curNode = Head;
var previousNode = null;
while (curNode.Next != null)
{
previousNode = curNode;
curNode = curNode.Next;
}
var lastNodeValue = curNode.Value;
if (previousNode == null)
Head = null;
else
previousNode.Next = null;
Size--;
return lastNodeValue;
}
return -1;
}
okay guys, after your help, I've rewritten this method that meets all the requirements and set to HeadNode null if there is only one node in linked list. So here we go:
public int RemoveLast()
{
if (HeadNode != null)
{
var currNode = HeadNode;
var prevNode = HeadNode;
if (HeadNode.Next == null)
{
HeadNode = null;
Size--;
return currNode.Value;
}
while (currNode.Next != null)
{
prevNode = currNode;
currNode = currNode.Next;
}
prevNode.Next = null;
Size--;
return currNode.Value;
}
return -1;
}
Thank you everyone who contributed in this thread. Happy Coding :)
This is my method to simply remove the node indicated, but how can I implement the DeleteBefore() and DeleteAfter() method that removes the node before (after) the node having the given node value.
public void DeleteAFter(T nodeVal)
{
Node<T> curr = front;
Node<T> prev = null;
// becomes true if we locate target
bool foundItem = false;
// scan until locate nodeVal or
// come to end of list
while (curr != null && !foundItem)
{
// have a match
if (curr.NodeValue.Equals(nodeVal))
{
// remove the first node
if (prev == null)
{
front = front.Next;
}
// erase intermediate node
else
{
prev.Next = curr.Next;
}
foundItem = true;
}
else
{
// advanced curr and prev
prev = curr;
curr = curr.Next;
}
I am writing a single linked list in C#, could you please suggest to me if there any way to write a better remove method than the one I have:
using System;
class Node
{
public int data = int.MinValue;
public Node m_NextNode;
public Node(int data_in)
{
data = data_in;
}
public Node()
{
}
}
class LinkedList
{
private Node m_HeadNode;
public void InsertData(int data)
{
Node aCurrentNode = m_HeadNode;
if(m_HeadNode == null)
{
m_HeadNode = new Node();
m_HeadNode.data = data;
}
else
{
while(aCurrentNode.m_NextNode != null)
aCurrentNode = aCurrentNode.m_NextNode;
aCurrentNode.m_NextNode = new Node();
aCurrentNode.m_NextNode.data = data;
}
}
public void DisplayData()
{
Node aCurrentNode = m_HeadNode;
while (aCurrentNode != null)
{
Console.WriteLine("the value is {0}", aCurrentNode.data);
aCurrentNode = aCurrentNode.m_NextNode;
}
}
public void RemoveData(int data)
{
Node aCurrentNode = m_HeadNode;
while (aCurrentNode != null)
{
//if the data is present in head
//remove the head and reset the head
if (m_HeadNode.data == data)
{
m_HeadNode = null;
m_HeadNode = aCurrentNode.m_NextNode;
}
else
{
//else save the previous node
Node previousNode = aCurrentNode;
if (aCurrentNode != null)
{
//store the current node
Node NextNode = aCurrentNode.m_NextNode;
if (NextNode != null)
{
//store the next node
Node tempNode = NextNode.m_NextNode;
if (NextNode.data == data)
{
previousNode.m_NextNode = tempNode;
NextNode = null;
}
}
aCurrentNode = aCurrentNode.m_NextNode;
}
}
}
}
}
class Program
{
static void Main(string[] args)
{
LinkedList aLinkedList = new LinkedList();
aLinkedList.InsertData(10);
aLinkedList.InsertData(20);
aLinkedList.InsertData(30);
aLinkedList.InsertData(40);
aLinkedList.DisplayData();
aLinkedList.RemoveData(10);
aLinkedList.RemoveData(40);
aLinkedList.RemoveData(20);
aLinkedList.RemoveData(30);
aLinkedList.DisplayData();
Console.Read();
}
}
I would pull the 'if removing the head node' out of the while loop, and make the while loop simpler. Just keep track of the current and previous nodes, and switch the reference when you find the node to remove.
public void RemoveData(int data)
{
if (m_HeadNode == null)
return;
if (m_HeadNode.data == data)
{
m_HeadNode = m_HeadNode.m_NextNode;
}
else
{
Node previous = m_HeadNode;
Node current = m_HeadNode.m_NextNode;
while (current != null)
{
if (current.data == data)
{
// If we're removing the last entry in the list, current.Next
// will be null. That's OK, because setting previous.Next to
// null is the proper way to set the end of the list.
previous.m_NextNode = current.m_NextNode;
break;
}
previous = current;
current = current.m_NextNode;
}
}
}
Is RemoveData supposed to remove one instance of that integer from the list, or all instances? The previous method removes just the first one, here's one that removes all of them.
public void RemoveAllData(int data)
{
while (m_HeadNode != null && m_HeadNode.data == data)
{
m_HeadNode = m_HeadNode.m_NextNode;
}
if(m_HeadNode != null)
{
Node previous = m_HeadNode;
Node current = m_HeadNode.m_NextNode;
while (current != null)
{
if (current.data == data)
{
// If we're removing the last entry in the list, current.Next
// will be null. That's OK, because setting previous.Next to
// null is the proper way to set the end of the list.
previous.m_NextNode = current.m_NextNode;
// If we remove the current node, then we don't need to move
// forward in the list. The reference to previous.Next, below,
// will now point one element forward than it did before.
}
else
{
// Only move forward in the list if we actually need to,
// if we didn't remove an item.
previous = current;
}
current = previous.m_NextNode;
}
}
}
You have a line you do not need:
m_HeadNode = null;
m_HeadNode = aCurrentNode.m_NextNode;
You don't need to set m_HeadNode to null before you set it to something else.
public bool RemoveNode(int data) {
Node prev = null;
for (Node node = head; node != null; node = node.next) {
if (node.data == data) {
if (prev == null) head = node.next;
else prev.next = node.next;
return true;
}
prev = node;
}
return false;
}
public void RemoveData(int data)
{
if(null == m_HeadNode) return;
if(m_HeadNode.data == data)
{
// remove first node
}
else
{
Node current = m_HeadNode;
while((null != current.m_NextNode) && (current.m_NextNode.data != data))
current = current.m_NextNode;
if(null != current.m_NextNode)
{
// do remove node (since this sounds like homework, I'll leave that to you)
}
}
}
with only one local variable.
There is a bug in you code, imagine you have list that has 3 elements with data = 5 and you want to remove 5, you codes stores the head in aCurrentNode and starts the loop. There the condition is true so you move the head to the next. but aCurrentNode is not updated so in the next iteration it's pointing to the previous Head and aCurrentNode.m_NextNod would be your current Head, Hence you got yourself in a never ending loop!
public void Remove(int data)
{
for(var cur = new Node {Next = Head}; cur.Next != null; cur = cur.Next)
{
if (cur.Next.Data != data) continue;
if (cur.Next == Head)
Head = Head.Next;
else
cur.Next = cur.Next.Next;
}
}
a trick to make you loop simpler is to start with a fake node that points to head. This way you don't need to place an If to check head differently, however you need an if to set the head. the other trick is to check for next nodes data. that way you don't need to keep a previous Node.
public SLElement Remove(int index)
{
SLElement prev = _root;
if (prev == null) return null;
SLElement curr = _root._next;
for (int i = 1; i < index; i++)
{
if (curr == null) return null;
prev = curr;
curr = curr._next;
}
prev._next = curr._next;
curr._next = null;
return curr;
}
This deletes the element with a specific index, not with a specific value.
To Make really simple. Please follow the link. Below is a code snippet to remove item from a single link list.
public void DeleteNode(int nodeIndex)
{
int indexCounter = 0;
Node TempNode = StartNode;
Node PreviousNode = null;
while (TempNode.AddressHolder != null)
{
if (indexCounter == nodeIndex)
{
PreviousNode.AddressHolder = TempNode.AddressHolder;
break;
}
indexCounter++;
PreviousNode = TempNode;
TempNode = TempNode.AddressHolder;
}
}