# Linked List - Delete last node by key

In this method, last node in the linked list with specified key (value) is deleted. For example - if the given List is 10->20->30->20->40 and the last occurrence of 20 is deleted, the Linked List becomes 10->20->30->40.

If the head of the linked list is not null, create three nodes: 1. lastNode - to track the last node with value equal to key, 2. previousToLast - to track node previous to lastNode, and 3. temp - to traverse through the list. Then traverse the list to its end while updating lastNode and previousToLast whenever find a node with value equal to the specified key. At last delete lastNode and update links accordingly.

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

```void pop_last(int key) {

//1. if head is not null create three nodes
//   lastNode - to track last node with value
//   equal to key, previousToLast - to track
//   node previous to lastNode, temp - to
//   traverse through the list
Node *previousToLast, *lastNode, *temp;
previousToLast = NULL;
lastNode = NULL;

//2. traverse through the list and keep on updating
//   lastNode and previousToLast whenever find a node
//   with value equal to the specified key

while(temp->next != NULL) {
if(temp->next->data == key) {
previousToLast = temp;
lastNode = temp->next;
}
temp = temp->next;
}

//3. Delete the lastNode and update all links
if(lastNode != NULL) {
free(lastNode);
} else {
previousToLast->next = lastNode->next;
free(lastNode);
}
}
}
}
```
```void pop_last(struct Node** head_ref, int key) {

//1. if head is not null create three nodes
//   lastNode - to track last node with value
//   equal to key, previousToLast - to track
//   node previous to lastNode, temp - to
//   traverse through the list
struct Node *previousToLast, *lastNode, *temp;
previousToLast = NULL;
lastNode = NULL;

//2. traverse through the list and keep on updating
//   lastNode and previousToLast whenever find a node
//   with value equal to the specified key

while(temp->next != NULL) {
if(temp->next->data == key) {
previousToLast = temp;
lastNode = temp->next;
}
temp = temp->next;
}

//3. Delete the lastNode and update all links
if(lastNode != NULL) {
free(lastNode);
} else {
previousToLast->next = lastNode->next;
free(lastNode);
}
}
}
}
```
```def pop_last(self, key):

#1. if head is not null create three nodes
#   lastNode - to track last node with value
#   equal to key, previousToLast - to track
#   node previous to lastNode, temp - to
#   traverse through the list
temp = None
previousToLast = None
lastNode = None

#2. traverse through the list and keep on updating
#   lastNode and previousToLast whenever find a node
#   with value equal to the specified key

while(temp.next != None):
if(temp.next.data == key):
previousToLast = temp
lastNode = temp.next
temp = temp.next

#3. Delete the lastNode and update all links
if(lastNode != None):
lastNode = None
else:
previousToLast.next = lastNode.next
lastNode = None
```
```void pop_last(int key) {

//1. if head is not null create three nodes
//   lastNode - to track last node with value
//   equal to key, previousToLast - to track
//   node previous to lastNode, temp - to
//   traverse through the list
Node previousToLast, lastNode, temp;
previousToLast = null;
lastNode = null;

//2. traverse through the list and keep on updating
//   lastNode and previousToLast whenever find a node
//   with value equal to the specified key

while(temp.next != null) {
if(temp.next.data == key) {
previousToLast = temp;
lastNode = temp.next;
}
temp = temp.next;
}

//3. Delete the lastNode and update all links
if(lastNode != null) {
lastNode = null;
} else {
previousToLast.next = lastNode.next;
lastNode = null;
}
}
}
}
```
```public void pop_last(int key) {

//1. if head is not null create three nodes
//   lastNode - to track last node with value
//   equal to key, previousToLast - to track
//   node previous to lastNode, temp - to
//   traverse through the list
Node previousToLast, lastNode, temp;
previousToLast = null;
lastNode = null;

//2. traverse through the list and keep on updating
//   lastNode and previousToLast whenever find a node
//   with value equal to the specified key

while(temp.next != null) {
if(temp.next.data == key) {
previousToLast = temp;
lastNode = temp.next;
}
temp = temp.next;
}

//3. Delete the lastNode and update all links
if(lastNode != null) {
lastNode = null;
} else {
previousToLast.next = lastNode.next;
lastNode = null;
}
}
}
}
```
```public function pop_last(\$key) {

//1. if head is not null create three nodes
//   lastNode - to track last node with value
//   equal to key, previousToLast - to track
//   node previous to lastNode, temp - to
//   traverse through the list
\$temp = new Node();
\$previousToLast = null;
\$lastNode = null;

//2. traverse through the list and keep on updating
//   lastNode and previousToLast whenever find a node
//   with value equal to the specified key

while(\$temp->next != null) {
if(\$temp->next->data == \$key) {
\$previousToLast = \$temp;
\$lastNode = \$temp->next;
}
\$temp = \$temp->next;
}

//3. Delete the lastNode and update all links
if(\$lastNode != null) {
\$lastNode = null;
} else {
\$previousToLast->next = \$lastNode->next;
\$lastNode = null;
}
}
}
}
```

The below is a complete program that uses above discussed concept to delete last occurrence of the specified key (if exists) of the 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 last node by key
void pop_last(int key) {
Node *previousToLast, *lastNode, *temp;
previousToLast = NULL;
lastNode = NULL;

while(temp->next != NULL) {
if(temp->next->data == key) {
previousToLast = temp;
lastNode = temp->next;
}
temp = temp->next;
}

if(lastNode != NULL) {
free(lastNode);
} else {
previousToLast->next = lastNode->next;
free(lastNode);
}
}
}
}

//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(20);
MyList.push_back(40);
MyList.PrintList();

//Delete last occurrence of 20
MyList.pop_last(20);
MyList.PrintList();

return 0;
}
```

The above code will give the following output:

```The list contains: 10 20 30 20 40
The list contains: 10 20 30 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 last node by key
void pop_last(struct Node** head_ref, int key) {
struct Node *previousToLast, *lastNode, *temp;
previousToLast = NULL;
lastNode = NULL;

while(temp->next != NULL) {
if(temp->next->data == key) {
previousToLast = temp;
lastNode = temp->next;
}
temp = temp->next;
}

if(lastNode != NULL) {
free(lastNode);
} else {
previousToLast->next = lastNode->next;
free(lastNode);
}
}
}
}

//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, 20);
push_back(&MyList, 40);
PrintList(MyList);

//Delete last occurrence of 20
pop_last(&MyList, 20);
PrintList(MyList);

return 0;
}
```

The above code will give the following output:

```The list contains: 10 20 30 20 40
The list contains: 10 20 30 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 last node by key
def pop_last(self, key):
temp = None
previousToLast = None
lastNode = None

while(temp.next != None):
if(temp.next.data == key):
previousToLast = temp
lastNode = temp.next
temp = temp.next

if(lastNode != None):
lastNode = None
else:
previousToLast.next = lastNode.next
lastNode = None

#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(20)
MyList.push_back(40)
MyList.PrintList()

#Delete last occurrence of 20
MyList.pop_last(20)
MyList.PrintList()
```

The above code will give the following output:

```The list contains: 10 20 30 20 40
The list contains: 10 20 30 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 last node by key
void pop_last(int key) {
Node previousToLast, lastNode, temp;
previousToLast = null;
lastNode = null;

while(temp.next != null) {
if(temp.next.data == key) {
previousToLast = temp;
lastNode = temp.next;
}
temp = temp.next;
}

if(lastNode != null) {
lastNode = null;
} else {
previousToLast.next = lastNode.next;
lastNode = null;
}
}
}
}

//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(20);
MyList.push_back(40);
MyList.PrintList();

//Delete last occurrence of 20
MyList.pop_last(20);
MyList.PrintList();
}
}
```

The above code will give the following output:

```The list contains: 10 20 30 20 40
The list contains: 10 20 30 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 last node by key
public void pop_last(int key) {
Node previousToLast, lastNode, temp;
previousToLast = null;
lastNode = null;

while(temp.next != null) {
if(temp.next.data == key) {
previousToLast = temp;
lastNode = temp.next;
}
temp = temp.next;
}

if(lastNode != null) {
lastNode = null;
} else {
previousToLast.next = lastNode.next;
lastNode = null;
}
}
}
}

//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(20);
MyList.push_back(40);
MyList.PrintList();

//Delete last occurrence of 20
MyList.pop_last(20);
MyList.PrintList();
}
}
```

The above code will give the following output:

```The list contains: 10 20 30 20 40
The list contains: 10 20 30 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 last node by key
public function pop_last(\$key) {
\$temp = new Node();
\$previousToLast = null;
\$lastNode = null;

while(\$temp->next != null) {
if(\$temp->next->data == \$key) {
\$previousToLast = \$temp;
\$lastNode = \$temp->next;
}
\$temp = \$temp->next;
}

if(\$lastNode != null) {
\$lastNode = null;
} else {
\$previousToLast->next = \$lastNode->next;
\$lastNode = null;
}
}
}
}

//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(20);
\$MyList->push_back(40);
\$MyList->PrintList();

//Delete last occurrence of 20
\$MyList->pop_last(20);
\$MyList->PrintList();
?>
```

The above code will give the following output:

```The list contains: 10 20 30 20 40
The list contains: 10 20 30 40
```

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