# Linked List - Delete odd nodes

Deleting odd nodes of a linked list requires traverse through the list and deleting odd nodes one by one. If the list is not null then release the head and make next of head as new head. If the new head is not null then create two nodes - evenNode and oddNode. Make evenNode to the first even node of list and oddNode to second odd node of the list (3rd node in the original list). If both are not null, delete the oddNode and adjust links. Move both nodes to next set of even-odd nodes. Repeat the process till the any or both nodes become null.

The function deleteOddNodes is created for this purpose. It is a 5-step process.

```void deleteOddNodes() {

free(temp);

//2. if the new head is not null create
//   nodes - evenNode and oddNode

while(evenNode != NULL && oddNode != NULL) {

//3. while evenNode and oddNode are not null
//   make next of evenNode as next of oddNode
//   and free oddNode
evenNode->next = oddNode->next;
free(oddNode);

//4. and make evenNode as next of evenNode
evenNode = evenNode->next;

//5. Update evenNode and oddNode
if(evenNode != NULL)
oddNode = evenNode->next;
}
}
}
}
```
```void deleteOddNodes(struct Node** head_ref) {

free(temp);

//2. if the new head is not null create
//   nodes - evenNode and oddNode

while(evenNode != NULL && oddNode != NULL) {

//3. while evenNode and oddNode are not null
//   make next of evenNode as next of oddNode
//   and free oddNode
evenNode->next = oddNode->next;
free(oddNode);

//4. and make evenNode as next of evenNode
evenNode = evenNode->next;

//5. Update evenNode and oddNode
if(evenNode != NULL)
oddNode = evenNode->next;
}
}
}
}
```
```def deleteOddNodes(self):

temp = None

#2. if the new head is not null create
#   nodes - evenNode and oddNode

while(evenNode != None and oddNode != None):

#3. while evenNode and oddNode are not null
#   make next of evenNode as next of oddNode
#   and free oddNode
evenNode.next = oddNode.next
oddNode = None

#4. and make evenNode as next of evenNode
evenNode = evenNode.next

#5. Update evenNode and oddNode
if(evenNode != None):
oddNode = evenNode.next
```
```void deleteOddNodes() {

temp = null;

//2. if the new head is not null create
//   nodes - evenNode and oddNode

while(evenNode != null && oddNode != null) {

//3. while evenNode and oddNode are not null
//   make next of evenNode as next of oddNode
//   and free oddNode
evenNode.next = oddNode.next;
oddNode = null;

//4. and make evenNode as next of evenNode
evenNode = evenNode.next;

//5. Update evenNode and oddNode
if(evenNode != null)
oddNode = evenNode.next;
}
}
}
}
```
```public void deleteOddNodes() {

temp = null;

//2. if the new head is not null create
//   nodes - evenNode and oddNode

while(evenNode != null && oddNode != null) {

//3. while evenNode and oddNode are not null
//   make next of evenNode as next of oddNode
//   and free oddNode
evenNode.next = oddNode.next;
oddNode = null;

//4. and make evenNode as next of evenNode
evenNode = evenNode.next;

//5. Update evenNode and oddNode
if(evenNode != null)
oddNode = evenNode.next;
}
}
}
}
```
```public function deleteOddNodes() {

\$temp = null;

//2. if the new head is not null create
//   nodes - evenNode and oddNode

while(\$evenNode != null && \$oddNode != null) {

//3. while evenNode and oddNode are not null
//   make next of evenNode as next of oddNode
//   and free oddNode
\$evenNode->next = \$oddNode->next;
\$oddNode = null;

//4. and make evenNode as next of evenNode
\$evenNode = \$evenNode->next;

//5. Update evenNode and oddNode
if(\$evenNode != null)
\$oddNode = \$evenNode->next;
}
}
}
}
```

The below is a complete program that uses above discussed concept of deleting odd nodes of a 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 {
while(temp->next != NULL)
temp = temp->next;
temp->next = newNode;
}
}

//delete odd nodes of the list
void deleteOddNodes() {
free(temp);
while(evenNode != NULL && oddNode != NULL) {
evenNode->next = oddNode->next;
free(oddNode);
evenNode = evenNode->next;
if(evenNode != NULL)
oddNode = evenNode->next;
}
}
}
}

//display the content of the list
void PrintList() {
if(temp != NULL) {
cout<<"The list contains: ";
while(temp != NULL) {
cout<<temp->data<<" ";
temp = temp->next;
}
cout<<"\n";
} 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 odd nodes of the list
MyList.deleteOddNodes();

cout<<"After deleting odd 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 odd nodes.
The list contains: 20 40
```
```#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 {
while(temp->next != NULL) {
temp = temp->next;
}
temp->next = newNode;
}
}

//delete odd nodes of the list
free(temp);
while(evenNode != NULL && oddNode != NULL) {
evenNode->next = oddNode->next;
free(oddNode);
evenNode = evenNode->next;
if(evenNode != NULL)
oddNode = evenNode->next;
}
}
}
}

//display the content of the list
printf("The list contains: ");
while (temp != NULL) {
printf("%i ",temp->data);
temp = temp->next;
}
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 odd nodes of the list
deleteOddNodes(&MyList);

printf("After deleting odd 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 odd nodes.
The list contains: 20 40
```
```# 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:
while(temp.next != None):
temp = temp.next
temp.next = newNode

#delete odd nodes of the list
def deleteOddNodes(self):
temp = None
while(evenNode != None and oddNode != None):
evenNode.next = oddNode.next
oddNode = None
evenNode = evenNode.next
if(evenNode != None):
oddNode = evenNode.next

#display the content of the list
def PrintList(self):
if(temp != None):
print("The list contains:", end=" ")
while (temp != None):
print(temp.data, end=" ")
temp = temp.next
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 odd nodes of the list
MyList.deleteOddNodes()

print("After deleting odd 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 odd nodes.
The list contains: 20 40
```
```//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();
while(temp.next != null)
temp = temp.next;
temp.next = newNode;
}
}

//delete odd nodes of the list
void deleteOddNodes() {
temp = null;
while(evenNode != null && oddNode != null) {
evenNode.next = oddNode.next;
oddNode = null;
evenNode = evenNode.next;
if(evenNode != null)
oddNode = evenNode.next;
}
}
}
}

//display the content of the list
void PrintList() {
Node temp = new Node();
if(temp != null) {
System.out.print("The list contains: ");
while(temp != null) {
System.out.print(temp.data + " ");
temp = temp.next;
}
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 odd nodes of the list
MyList.deleteOddNodes();

System.out.println("After deleting odd 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 odd nodes.
The list contains: 20 40
```
```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();
while(temp.next != null)
temp = temp.next;
temp.next = newNode;
}
}

//delete odd nodes of the list
public void deleteOddNodes() {
temp = null;
while(evenNode != null && oddNode != null) {
evenNode.next = oddNode.next;
oddNode = null;
evenNode = evenNode.next;
if(evenNode != null)
oddNode = evenNode.next;
}
}
}
}

//display the content of the list
public void PrintList() {
Node temp = new Node();
if(temp != null) {
Console.Write("The list contains: ");
while(temp != null) {
Console.Write(temp.data + " ");
temp = temp.next;
}
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 odd nodes of the list
MyList.deleteOddNodes();

Console.WriteLine("After deleting odd 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 odd nodes.
The list contains: 20 40
```
```<?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();
while(\$temp->next != null) {
\$temp = \$temp->next;
}
\$temp->next = \$newNode;
}
}

//delete odd nodes of the list
public function deleteOddNodes() {
\$temp = null;
while(\$evenNode != null && \$oddNode != null) {
\$evenNode->next = \$oddNode->next;
\$oddNode = null;
\$evenNode = \$evenNode->next;
if(\$evenNode != null)
\$oddNode = \$evenNode->next;
}
}
}
}

//display the content of the list
public function PrintList() {
\$temp = new Node();
if(\$temp != null) {
echo "The list contains: ";
while(\$temp != null) {
echo \$temp->data." ";
\$temp = \$temp->next;
}
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 odd nodes of the list
\$MyList->deleteOddNodes();

echo "After deleting odd 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 odd nodes.
The list contains: 20 40
```

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