# Doubly Linked List - Delete all nodes by key

In this method, all nodes in the doubly linked list with specified key (value) is deleted. For example - if the given list is 10->20->30->10->20 and all occurrences of 20 are deleted, the list becomes 10->30->10.

If the head of the doubly linked list is not null and the value stored at head is equal to key, then adjust the head as head next, delete previous head and adjust links. Keep on doing the same process until the new head becomes null or not equal to the key. After that create a temp node to traverse through the list and delete those nodes with value equal to the key and adjust links accordingly.

The function pop_all is created for this purpose. It is a 2-step process.

```void pop_all(int key) {
Node* nodeToDelete;

//1. if the head is not null and value stored at head
//   until new head becomes null or not equal to key
free(nodeToDelete);
}

//2. create a temp node to traverse through the
//   list and delete nodes with value equal to
if(temp != NULL) {
while(temp->next != NULL) {
if(temp->next->data == key) {
nodeToDelete = temp->next;
temp->next = temp->next->next;
if(temp->next != NULL)
temp->next->prev = temp;
free(nodeToDelete);
} else {
temp = temp->next;
}
}
}
}
```
```void pop_all(struct Node** head_ref, int key) {
struct Node* nodeToDelete;

//1. if the head is not null and value stored at head
//   until new head becomes null or not equal to key
free(nodeToDelete);
}

//2. create a temp node to traverse through the
//   list and delete nodes with value equal to
if(temp != NULL) {
while(temp->next != NULL) {
if(temp->next->data == key) {
nodeToDelete = temp->next;
temp->next = temp->next->next;
if(temp->next != NULL)
temp->next->prev = temp;
free(nodeToDelete);
} else {
temp = temp->next;
}
}
}
}
```
```def pop_all(self, key):

#1. if the head is not null and value stored at head
#   until new head becomes null or not equal to key
nodeToDelete = None

#2. create a temp node to traverse through the
#   list and delete nodes with value equal to
if(temp != None):
while(temp.next != None):
if(temp.next.data == key):
nodeToDelete = temp.next
temp.next = temp.next.next
if(temp.next != None):
temp.next.prev = temp
nodeToDelete = None
else:
temp = temp.next
```
```void pop_all(int key) {
Node nodeToDelete = new Node();

//1. if the head is not null and value stored at head
//   until new head becomes null or not equal to key
nodeToDelete = null;
}

//2. create a temp node to traverse through the
//   list and delete nodes with value equal to
if(temp != null) {
while(temp.next != null) {
if(temp.next.data == key) {
nodeToDelete = temp.next;
temp.next = temp.next.next;
if(temp.next != null)
temp.next.prev = temp;
nodeToDelete = null;
} else {
temp = temp.next;
}
}
}
}
```
```public void pop_all(int key) {
Node nodeToDelete = new Node();

//1. if the head is not null and value stored at head
//   until new head becomes null or not equal to key
nodeToDelete = null;
}

//2. create a temp node to traverse through the
//   list and delete nodes with value equal to
if(temp != null) {
while(temp.next != null) {
if(temp.next.data == key) {
nodeToDelete = temp.next;
temp.next = temp.next.next;
if(temp.next != null)
temp.next.prev = temp;
nodeToDelete = null;
} else {
temp = temp.next;
}
}
}
}
```
```public function pop_all(\$key) {
\$nodeToDelete = new Node();

//1. if the head is not null and value stored at head
//   until new head becomes null or not equal to key
\$nodeToDelete = null;
}

//2. create a temp node to traverse through the
//   list and delete nodes with value equal to
if(\$temp != null) {
while(\$temp->next != null) {
if(\$temp->next->data == \$key) {
\$nodeToDelete = \$temp->next;
\$temp->next = \$temp->next->next;
if(\$temp->next != null)
\$temp->next->prev = \$temp;
\$nodeToDelete = null;
} else {
\$temp = \$temp->next;
}
}
}
}
```

The below is a complete program that uses above discussed concept to delete all occurrences of the specified key (if exists) of the doubly linked list.

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

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

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;
newNode->prev = NULL;
} else {
while(temp->next != NULL)
temp = temp->next;
temp->next = newNode;
newNode->prev = temp;
}
}

//Delete all nodes by key
void pop_all(int key) {
Node* nodeToDelete;
free(nodeToDelete);
}

if(temp != NULL) {
while(temp->next != NULL) {
if(temp->next->data == key) {
nodeToDelete = temp->next;
temp->next = temp->next->next;
if(temp->next != NULL)
temp->next->prev = temp;
free(nodeToDelete);
} else {
temp = temp->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 at the end of the list.
MyList.push_back(10);
MyList.push_back(20);
MyList.push_back(30);
MyList.push_back(10);
MyList.push_back(20);
MyList.PrintList();

//Delete all occurrences of 20
MyList.pop_all(20);
MyList.PrintList();

return 0;
}
```

The above code will give the following output:

```The list contains: 10 20 30 10 20
The list contains: 10 30 10
```
```#include <stdio.h>
#include <stdlib.h>

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

//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;
newNode->prev = NULL;
} else {
while(temp->next != NULL) {
temp = temp->next;
}
temp->next = newNode;
newNode->prev = temp;
}
}

//Delete all nodes by key
void pop_all(struct Node** head_ref, int key) {
struct Node* nodeToDelete;
free(nodeToDelete);
}

if(temp != NULL) {
while(temp->next != NULL) {
if(temp->next->data == key) {
nodeToDelete = temp->next;
temp->next = temp->next->next;
if(temp->next != NULL)
temp->next->prev = temp;
free(nodeToDelete);
} else {
temp = temp->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 at the end of the list.
push_back(&MyList, 10);
push_back(&MyList, 20);
push_back(&MyList, 30);
push_back(&MyList, 10);
push_back(&MyList, 20);
PrintList(MyList);

//Delete all occurrences of 20
pop_all(&MyList, 20);
PrintList(MyList);

return 0;
}
```

The above code will give the following output:

```The list contains: 10 20 30 10 20
The list contains: 10 30 10
```
```# node structure
class Node:
def __init__(self, data):
self.data = data
self.next = None
self.prev = 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
newNode.prev = temp

#Delete all nodes by key
def pop_all(self, key):
nodeToDelete = None

if(temp != None):
while(temp.next != None):
if(temp.next.data == key):
nodeToDelete = temp.next
temp.next = temp.next.next
if(temp.next != None):
temp.next.prev = temp
nodeToDelete = None
else:
temp = temp.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 at the end of the list.
MyList.push_back(10)
MyList.push_back(20)
MyList.push_back(30)
MyList.push_back(10)
MyList.push_back(20)
MyList.PrintList()

#Delete all occurrences of 20
MyList.pop_all(20)
MyList.PrintList()
```

The above code will give the following output:

```The list contains: 10 20 30 10 20
The list contains: 10 30 10
```
```//node structure
class Node {
int data;
Node next;
Node prev;
};

}

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

//Delete all nodes by key
void pop_all(int key) {
Node nodeToDelete = new Node();
nodeToDelete = null;
}

if(temp != null) {
while(temp.next != null) {
if(temp.next.data == key) {
nodeToDelete = temp.next;
temp.next = temp.next.next;
if(temp.next != null)
temp.next.prev = temp;
nodeToDelete = null;
} else {
temp = temp.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 at the end of the list.
MyList.push_back(10);
MyList.push_back(20);
MyList.push_back(30);
MyList.push_back(10);
MyList.push_back(20);
MyList.PrintList();

//Delete all occurrences of 20
MyList.pop_all(20);
MyList.PrintList();
}
}
```

The above code will give the following output:

```The list contains: 10 20 30 10 20
The list contains: 10 30 10
```
```using System;

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

}

//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;
newNode.prev = null;
} else {
Node temp = new Node();
while(temp.next != null)
temp = temp.next;
temp.next = newNode;
newNode.prev = temp;
}
}

//Delete all nodes by key
public void pop_all(int key) {
Node nodeToDelete = new Node();
nodeToDelete = null;
}

if(temp != null) {
while(temp.next != null) {
if(temp.next.data == key) {
nodeToDelete = temp.next;
temp.next = temp.next.next;
if(temp.next != null)
temp.next.prev = temp;
nodeToDelete = null;
} else {
temp = temp.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 at the end of the list.
MyList.push_back(10);
MyList.push_back(20);
MyList.push_back(30);
MyList.push_back(10);
MyList.push_back(20);
MyList.PrintList();

//Delete all occurrences of 20
MyList.pop_all(20);
MyList.PrintList();
}
}
```

The above code will give the following output:

```The list contains: 10 20 30 10 20
The list contains: 10 30 10
```
```<?php
//node structure
class Node {
public \$data;
public \$next;
public \$prev;
}

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;
\$newNode->prev = null;
} else {
\$temp = new Node();
while(\$temp->next != null) {
\$temp = \$temp->next;
}
\$temp->next = \$newNode;
\$newNode->prev = \$temp;
}
}

//Delete all nodes by key
public function pop_all(\$key) {
\$nodeToDelete = new Node();
\$nodeToDelete = null;
}

if(\$temp != null) {
while(\$temp->next != null) {
if(\$temp->next->data == \$key) {
\$nodeToDelete = \$temp->next;
\$temp->next = \$temp->next->next;
if(\$temp->next != null)
\$temp->next->prev = \$temp;
\$nodeToDelete = null;
} else {
\$temp = \$temp->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 at the end of the list.
\$MyList->push_back(10);
\$MyList->push_back(20);
\$MyList->push_back(30);
\$MyList->push_back(10);
\$MyList->push_back(20);
\$MyList->PrintList();

//Delete all occurrences of 20
\$MyList->pop_all(20);
\$MyList->PrintList();
?>
```

The above code will give the following output:

```The list contains: 10 20 30 10 20
The list contains: 10 30 10
```

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