# Circular Singly Linked List - Delete even nodes

Deleting even nodes of a circular singly linked list requires traverse through the list and deleting even nodes one by one. It requires creating two nodes - oddNode and evenNode. If the list contains more than one node, make oddNode to first odd node of list and evenNode to first even node of the list. Store the current odd node into temp node and delete the even node. Move both nodes to next set of odd-even nodes. Repeat the process till any of nodes reaches head. Finally, link the last node with the head.

The function deleteEvenNodes is created for this purpose. It is a 3-step process.

```void deleteEvenNodes() {

//1. if the list has more than one element
//   create evenNode node - pointing to head
//   oddNode node - pointing to next of head
//   temp node - to store last odd node
Node* temp = new Node();

while(true) {

//2. delete even node and update evenNode and
//   oddNode to next set of odd-even nodes
//   update temp node to latest oddNode node
//   continue the process till any of the node
temp = oddNode;
oddNode->next = evenNode->next;
free(evenNode);
oddNode = oddNode->next;
evenNode = oddNode->next;
break;
}

//3. if oddNode reaches head, make next of
//   temp as head else make next of oddNode
else
}
}
```
```void deleteEvenNodes(struct Node** head_ref) {

//1. if the list has more than one element
//   create evenNode node - pointing to head
//   oddNode node - pointing to next of head
//   temp node - to store last odd node
struct Node* temp;

while(1) {

//2. delete even node and update evenNode and
//   oddNode to next set of odd-even nodes
//   update temp node to latest oddNode node
//   continue the process till any of the node
temp = oddNode;
oddNode->next = evenNode->next;
free(evenNode);
oddNode = oddNode->next;
evenNode = oddNode->next;
break;
}

//3. if oddNode reaches head, make next of
//   temp as head else make next of oddNode
else
}
}
```
```def deleteEvenNodes(self):
#1. if the list has more than one element
#   create evenNode node - pointing to head
#   oddNode node - pointing to next of head
#   temp node - to store last odd node

while(True):

#2. delete even node and update evenNode and
#   oddNode to next set of odd-even nodes
#   update temp node to latest oddNode node
#   continue the process till any of the node
temp = oddNode
oddNode.next = evenNode.next
evenNode = None
oddNode = oddNode.next
evenNode = oddNode.next
break

#3. if oddNode reaches head, make next of
#   temp as head else make next of oddNode
else:
```
```void deleteEvenNodes() {

//1. if the list has more than one element
//   create evenNode node - pointing to head
//   oddNode node - pointing to next of head
//   temp node - to store last odd node
Node temp = new Node();

while(true) {

//2. delete even node and update evenNode and
//   oddNode to next set of odd-even nodes
//   update temp node to latest oddNode node
//   continue the process till any of the node
temp = oddNode;
oddNode.next = evenNode.next;
evenNode = null;
oddNode = oddNode.next;
evenNode = oddNode.next;
break;
}

//3. if oddNode reaches head, make next of
//   temp as head else make next of oddNode
else
}
}
```
```public void deleteEvenNodes() {

//1. if the list has more than one element
//   create evenNode node - pointing to head
//   oddNode node - pointing to next of head
//   temp node - to store last odd node
Node temp = new Node();

while(true) {

//2. delete even node and update evenNode and
//   oddNode to next set of odd-even nodes
//   update temp node to latest oddNode node
//   continue the process till any of the node
temp = oddNode;
oddNode.next = evenNode.next;
evenNode = null;
oddNode = oddNode.next;
evenNode = oddNode.next;
break;
}

//3. if oddNode reaches head, make next of
//   temp as head else make next of oddNode
else
}
}
```
```public function deleteEvenNodes() {

//1. if the list has more than one element
//   create evenNode node - pointing to head
//   oddNode node - pointing to next of head
//   temp node - to store last odd node
\$temp = new Node();

while(true) {

//2. delete even node and update evenNode and
//   oddNode to next set of odd-even nodes
//   update temp node to latest oddNode node
//   continue the process till any of the node
\$temp = \$oddNode;
\$oddNode->next = \$evenNode->next;
\$evenNode = null;
\$oddNode = \$oddNode->next;
\$evenNode = \$oddNode->next;
break;
}

//3. if oddNode reaches head, make next of
//   temp as head else make next of oddNode
else
}
}
```

The below is a complete program that uses above discussed concept of deleting even nodes of a circular singly linked list.

```#include <iostream>
using namespace std;

//node structure
struct Node {
int data;
Node* next;
};

private:
public:
}

//Add new element at the end of the list
void push_back(int newElement) {
Node* newNode = new Node();
newNode->data = newElement;
newNode->next = NULL;
} else {
temp = temp->next;
temp->next = newNode;
}
}

//delete even nodes of the list
void deleteEvenNodes() {
Node* temp = new Node();
while(true) {
temp = oddNode;
oddNode->next = evenNode->next;
free(evenNode);
oddNode = oddNode->next;
evenNode = oddNode->next;
break;
}
else
}
}

//display the content of the list
void PrintList() {
if(temp != NULL) {
cout<<"The list contains: ";
while(true) {
cout<<temp->data<<" ";
temp = temp->next;
break;
}
cout<<endl;
} else {
cout<<"The list is empty.\n";
}
}
};

// test the code
int main() {

//Add five elements in the list.
MyList.push_back(10);
MyList.push_back(20);
MyList.push_back(30);
MyList.push_back(40);
MyList.push_back(50);

//Display the content of the list.
MyList.PrintList();

//delete even nodes of the list
MyList.deleteEvenNodes();

cout<<"After deleting even nodes.\n";
//Display the content of the list.
MyList.PrintList();

return 0;
}
```

The above code will give the following output:

```The list contains: 10 20 30 40 50
After deleting even nodes.
The list contains: 10 30 50
```
```#include <stdio.h>
#include <stdlib.h>

//node structure
struct Node {
int data;
struct Node* next;
};

//Add new element at the end of the list
void push_back(struct Node** head_ref, int newElement) {
struct Node *newNode, *temp;
newNode = (struct Node*)malloc(sizeof(struct Node));
newNode->data = newElement;
newNode->next = NULL;
} else {
temp = temp->next;
}
temp->next = newNode;
}
}

//delete even nodes of the list
struct Node* temp;
while(1) {
temp = oddNode;
oddNode->next = evenNode->next;
free(evenNode);
oddNode = oddNode->next;
evenNode = oddNode->next;
break;
}
else
}
}

//display the content of the list
printf("The list contains: ");
while (1) {
printf("%i ",temp->data);
temp = temp->next;
break;
}
printf("\n");
} else {
printf("The list is empty.\n");
}
}

// test the code
int main() {
struct Node* MyList = NULL;

//Add five elements in the list.
push_back(&MyList, 10);
push_back(&MyList, 20);
push_back(&MyList, 30);
push_back(&MyList, 40);
push_back(&MyList, 50);

//Display the content of the list.
PrintList(MyList);

//delete even nodes of the list
deleteEvenNodes(&MyList);

printf("After deleting even nodes.\n");
//Display the content of the list.
PrintList(MyList);

return 0;
}
```

The above code will give the following output:

```The list contains: 10 20 30 40 50
After deleting even nodes.
The list contains: 10 30 50
```
```# node structure
class Node:
def __init__(self, data):
self.data = data
self.next = None

def __init__(self):

#Add new element at the end of the list
def push_back(self, newElement):
newNode = Node(newElement)
return
else:
temp = temp.next
temp.next = newNode

#delete even nodes of the list
def deleteEvenNodes(self):
while(True):
temp = oddNode
oddNode.next = evenNode.next
evenNode = None
oddNode = oddNode.next
evenNode = oddNode.next
break
else:

#display the content of the list
def PrintList(self):
if(temp != None):
print("The list contains:", end=" ")
while (True):
print(temp.data, end=" ")
temp = temp.next
break
print()
else:
print("The list is empty.")

# test the code

#Add five elements in the list.
MyList.push_back(10)
MyList.push_back(20)
MyList.push_back(30)
MyList.push_back(40)
MyList.push_back(50)

#Display the content of the list.
MyList.PrintList()

#delete even nodes of the list
MyList.deleteEvenNodes()

print("After deleting even nodes.")
#Display the content of the list.
MyList.PrintList()
```

The above code will give the following output:

```The list contains: 10 20 30 40 50
After deleting even nodes.
The list contains: 10 30 50
```
```//node structure
class Node {
int data;
Node next;
};

}

//Add new element at the end of the list
void push_back(int newElement) {
Node newNode = new Node();
newNode.data = newElement;
newNode.next = null;
} else {
Node temp = new Node();
temp = temp.next;
temp.next = newNode;
}
}

//delete even nodes of the list
void deleteEvenNodes() {
Node temp = new Node();

while(true) {
temp = oddNode;
oddNode.next = evenNode.next;
evenNode = null;
oddNode = oddNode.next;
evenNode = oddNode.next;
break;
}
else
}
}

//display the content of the list
void PrintList() {
Node temp = new Node();
if(temp != null) {
System.out.print("The list contains: ");
while(true) {
System.out.print(temp.data + " ");
temp = temp.next;
break;
}
System.out.println();
} else {
System.out.println("The list is empty.");
}
}
};

// test the code
public class Implementation {
public static void main(String[] args) {

//Add five elements in the list.
MyList.push_back(10);
MyList.push_back(20);
MyList.push_back(30);
MyList.push_back(40);
MyList.push_back(50);

//Display the content of the list.
MyList.PrintList();

//delete even nodes of the list
MyList.deleteEvenNodes();

System.out.println("After deleting even nodes.");
//Display the content of the list.
MyList.PrintList();
}
}
```

The above code will give the following output:

```The list contains: 10 20 30 40 50
After deleting even nodes.
The list contains: 10 30 50
```
```using System;

//node structure
class Node {
public int data;
public Node next;
};

}

//Add new element at the end of the list
public void push_back(int newElement) {
Node newNode = new Node();
newNode.data = newElement;
newNode.next = null;
} else {
Node temp = new Node();
temp = temp.next;
temp.next = newNode;
}
}

//delete even nodes of the list
public void deleteEvenNodes() {
Node temp = new Node();

while(true) {
temp = oddNode;
oddNode.next = evenNode.next;
evenNode = null;
oddNode = oddNode.next;
evenNode = oddNode.next;
break;
}
else
}
}

//display the content of the list
public void PrintList() {
Node temp = new Node();
if(temp != null) {
Console.Write("The list contains: ");
while(true) {
Console.Write(temp.data + " ");
temp = temp.next;
break;
}
Console.WriteLine();
} else {
Console.WriteLine("The list is empty.");
}
}
};

// test the code
class Implementation {
static void Main(string[] args) {

//Add five elements in the list.
MyList.push_back(10);
MyList.push_back(20);
MyList.push_back(30);
MyList.push_back(40);
MyList.push_back(50);

//Display the content of the list.
MyList.PrintList();

//delete even nodes of the list
MyList.deleteEvenNodes();

Console.WriteLine("After deleting even nodes.");
//Display the content of the list.
MyList.PrintList();
}
}
```

The above code will give the following output:

```The list contains: 10 20 30 40 50
After deleting even nodes.
The list contains: 10 30 50
```
```<?php
//node structure
class Node {
public \$data;
public \$next;
}

public function __construct(){
}

//Add new element at the end of the list
public function push_back(\$newElement) {
\$newNode = new Node();
\$newNode->data = \$newElement;
\$newNode->next = null;
} else {
\$temp = new Node();
\$temp = \$temp->next;
}
\$temp->next = \$newNode;
}
}

//delete even nodes of the list
public function deleteEvenNodes() {
\$temp = new Node();

while(true) {
\$temp = \$oddNode;
\$oddNode->next = \$evenNode->next;
\$evenNode = null;
\$oddNode = \$oddNode->next;
\$evenNode = \$oddNode->next;
break;
}
else
}
}

//display the content of the list
public function PrintList() {
\$temp = new Node();
if(\$temp != null) {
echo "The list contains: ";
while(true) {
echo \$temp->data." ";
\$temp = \$temp->next;
break;
}
echo "\n";
} else {
echo "The list is empty.\n";
}
}
};

// test the code

//Add five elements in the list.
\$MyList->push_back(10);
\$MyList->push_back(20);
\$MyList->push_back(30);
\$MyList->push_back(40);
\$MyList->push_back(50);

//Display the content of the list.
\$MyList->PrintList();

//delete even nodes of the list
\$MyList->deleteEvenNodes();

echo "After deleting even nodes.\n";
//Display the content of the list.
\$MyList->PrintList();
?>
```

The above code will give the following output:

```The list contains: 10 20 30 40 50
After deleting even nodes.
The list contains: 10 30 50
```

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