# Delete nodes which have a greater value on right side using recursion

Given a singly linked list, remove all the nodes which have a greater value on the right side.

Examples:
a) The list 12->15->10->11->5->6->2->3->NULL should be changed to 15->11->6->3->NULL. Note that 12, 10, 5 and 2 have been deleted because there is a greater value on the right side.

When we examine 12, we see that after 12 there is one node with a value greater than 12 (i.e. 15), so we delete 12.
When we examine 15, we find no node after 15 that has a value greater than 15 so we keep this node.
When we go like this, we get 15->6->3

b) The list 10->20->30->40->50->60->NULL should be changed to 60->NULL. Note that 10, 20, 30, 40 and 50 have been deleted because they all have a greater value on the right side.

c) The list 60->50->40->30->20->10->NULL should not be changed.

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach: We have already solved this problem by using 2 loops and reversing linked list in the post Delete nodes which have a greater value on right side

Here we will discuss the solution without reversing the list. We will use recursion to solve this problem in which the base case would be when the head is pointing to NULL. Else we would be recursively calling function for the next node and updating max value if currentNode->data > currentMax. In this way, the whole list would be updated.

Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach ` `#include ` `using` `namespace` `std; ` ` `  `/* structure of a linked list node */` `struct` `Node { ` `    ``int` `data; ` `    ``struct` `Node* next; ` `}; ` ` `  `/*Utility function to find maximum value*/` `int` `maxVal(``int` `a, ``int` `b) ` `{ ` `    ``if` `(a > b) ` `        ``return` `a; ` `    ``return` `b; ` `} ` ` `  `/* Function to delete nodes which have  ` `a node with greater value node  ` `on left side */` `struct` `Node* delNodes(``struct` `Node* head, ``int``* max) ` `{ ` ` `  `    ``// Base case ` `    ``if` `(head == NULL) { ` `        ``return` `head; ` `    ``} ` ` `  `    ``head->next = delNodes(head->next, max); ` `    ``if` `(head->data < *max) { ` `        ``return` `head->next; ` `    ``} ` `    ``*max = maxVal(head->data, *max); ` `    ``return` `head; ` `} ` ` `  `/* Utility function to insert a node at the beginning */` `void` `push(``struct` `Node** head, ``int` `new_data) ` `{ ` `    ``struct` `Node* new_node = ``new` `Node; ` `    ``new_node->data = new_data; ` `    ``new_node->next = *head; ` `    ``*head = new_node; ` `} ` ` `  `/* Utility function to print a linked list */` `void` `printList(``struct` `Node* head) ` `{ ` `    ``while` `(head != NULL) { ` `        ``cout << head->data << ``" "``; ` `        ``head = head->next; ` `    ``} ` `    ``cout << endl; ` `} ` ` `  `/* Driver program to test above functions */` `int` `main() ` `{ ` `    ``struct` `Node* head = NULL; ` ` `  `    ``/* Create following linked list  ` `    ``12->15->10->11->5->6->2->3 */` `    ``push(&head, 3); ` `    ``push(&head, 2); ` `    ``push(&head, 6); ` `    ``push(&head, 5); ` `    ``push(&head, 11); ` `    ``push(&head, 10); ` `    ``push(&head, 15); ` `    ``push(&head, 12); ` ` `  `    ``cout << ``"Given Linked List"` `<< endl; ` `    ``printList(head); ` `    ``int` `max = INT_MIN; ` `    ``head = delNodes(head, &max); ` ` `  `    ``cout << ``"Modified Linked List"` `<< endl; ` `    ``printList(head); ` ` `  `    ``return` `0; ` `} `

## Java

 `// Java implementation of the approach  ` `class` `GFG  ` `{ ` ` `  `/* structure of a linked list node */` `static` `class` `Node ` `{  ` `    ``int` `data;  ` `    ``Node next;  ` `};  ` `static` `Node head; ` `static` `int` `max; ` ` `  `/*Utility function to find maximum value*/` `static` `int` `maxVal(``int` `a, ``int` `b)  ` `{  ` `    ``if` `(a > b)  ` `        ``return` `a;  ` `    ``return` `b;  ` `}  ` ` `  `/* Function to delete nodes which have  ` `a node with greater value node  ` `on left side */` `static` `Node delNodes(Node head)  ` `{  ` ` `  `    ``// Base case  ` `    ``if` `(head == ``null``)  ` `    ``{  ` `        ``return` `head;  ` `    ``}  ` ` `  `    ``head.next = delNodes(head.next);  ` `    ``if` `(head.data < max) ` `    ``{  ` `        ``return` `head.next;  ` `    ``}  ` `    ``max = maxVal(head.data, max);  ` `    ``return` `head;  ` `}  ` ` `  `/* Utility function to insert a node ` `at the beginning */` `static` `void` `push(Node head_ref,  ` `                 ``int` `new_data)  ` `{  ` `    ``Node new_node = ``new` `Node();  ` `    ``new_node.data = new_data;  ` `    ``new_node.next = head_ref;  ` `    ``head_ref = new_node;  ` `        ``head = head_ref; ` `}  ` ` `  `/* Utility function to print a linked list */` `static` `void` `printList(Node head)  ` `{  ` `    ``while` `(head != ``null``)  ` `    ``{  ` `        ``System.out.print(head.data + ``" "``);  ` `        ``head = head.next;  ` `    ``}  ` `    ``System.out.println();  ` `}  ` ` `  `// Driver Code ` `public` `static` `void` `main(String[] args)  ` `{ ` `    ``head = ``null``;  ` ` `  `    ``/* Create following linked list  ` `    ``12.15.10.11.5.6.2.3 */` `    ``push(head, ``3``);  ` `    ``push(head, ``2``);  ` `    ``push(head, ``6``);  ` `    ``push(head, ``5``);  ` `    ``push(head, ``11``);  ` `    ``push(head, ``10``);  ` `    ``push(head, ``15``);  ` `    ``push(head, ``12``);  ` ` `  `    ``System.out.println(``"Given Linked List"``);  ` `    ``printList(head);  ` `    ``max = Integer.MIN_VALUE;  ` `    ``head = delNodes(head);  ` ` `  `    ``System.out.println(``"Modified Linked List"``);  ` `    ``printList(head); ` `} ` `}  ` ` `  `// This code is contributed by 29AjayKumar `

## Python3

 `# Python3 program to reverse a linked ` `# list using a stack  ` ` `  `# Link list node  ` `class` `Node: ` `     `  `    ``def` `__init__(``self``, data, ``next``): ` `        ``self``.data ``=` `data ` `        ``self``.``next` `=` `next` ` `  `class` `LinkedList: ` `     `  `    ``def` `__init__(``self``): ` `        ``self``.head ``=` `None` `         `  `    ``# Function to push a new Node in ` `    ``# the linked list  ` `    ``def` `push(``self``, new_data):  ` `     `  `        ``new_node ``=` `Node(new_data, ``self``.head)  ` `        ``self``.head ``=` `new_node ` `     `  `    ``# Function to delete nodes which have a node ` `    ``# with greater value node on left side ` `    ``def` `delNodes(``self``, head):  ` `     `  `        ``# Base case  ` `        ``if` `head ``=``=` `None``:  ` `            ``return` `head ` `         `  `        ``global` `Max` `     `  `        ``head.``next` `=` `self``.delNodes(head.``next``) ` `        ``if` `head.data < ``Max``:  ` `            ``return` `head.``next` `         `  `        ``Max` `=` `max``(head.data, ``Max``)  ` `        ``return` `head  ` `     `  `    ``# Function to print the Linked list  ` `    ``def` `printList(``self``): ` `         `  `        ``curr ``=` `self``.head ` `        ``while` `curr:  ` `            ``print``(curr.data, end ``=` `" "``)  ` `            ``curr ``=` `curr.``next` `        ``print``() ` ` `  `# Driver Code  ` `if` `__name__ ``=``=` `"__main__"``: ` ` `  `    ``# Start with the empty list ` `    ``linkedList ``=` `LinkedList()  ` ` `  `    ``# Create following linked list  ` `    ``# 12->15->10->11->5->6->2->3  ` `    ``linkedList.push(``3``)  ` `    ``linkedList.push(``2``)  ` `    ``linkedList.push(``6``)  ` `    ``linkedList.push(``5``)  ` `    ``linkedList.push(``11``)  ` `    ``linkedList.push(``10``)  ` `    ``linkedList.push(``15``)  ` `    ``linkedList.push(``12``)  ` ` `  `    ``print``(``"Given Linked List"``) ` `    ``linkedList.printList()  ` `    ``Max` `=` `float``(``'-inf'``) ` `    ``linkedList.head ``=` `linkedList.delNodes(linkedList.head) ` ` `  `    ``print``(``"Modified Linked List"``) ` `     `  `    ``linkedList.printList()  ` ` `  `# This code is contributed by Rituraj Jain  `

## C#

 `// C# implementation of the approach ` `using` `System; ` ` `  `class` `GFG  ` `{ ` ` `  `/* structure of a linked list node */` `public` `class` `Node ` `{  ` `    ``public` `int` `data;  ` `    ``public` `Node next;  ` `};  ` `static` `Node head; ` `static` `int` `max; ` ` `  `/*Utility function to find maximum value*/` `static` `int` `maxVal(``int` `a, ``int` `b)  ` `{  ` `    ``if` `(a > b)  ` `        ``return` `a;  ` `    ``return` `b;  ` `}  ` ` `  `/* Function to delete nodes which have  ` `a node with greater value node  ` `on left side */` `static` `Node delNodes(Node head)  ` `{  ` ` `  `    ``// Base case  ` `    ``if` `(head == ``null``)  ` `    ``{  ` `        ``return` `head;  ` `    ``}  ` ` `  `    ``head.next = delNodes(head.next);  ` `    ``if` `(head.data < max) ` `    ``{  ` `        ``return` `head.next;  ` `    ``}  ` `    ``max = maxVal(head.data, max);  ` `    ``return` `head;  ` `}  ` ` `  `/* Utility function to insert a node ` `at the beginning */` `static` `void` `push(Node head_ref,  ` `                 ``int` `new_data)  ` `{  ` `    ``Node new_node = ``new` `Node();  ` `    ``new_node.data = new_data;  ` `    ``new_node.next = head_ref;  ` `    ``head_ref = new_node;  ` `        ``head = head_ref; ` `}  ` ` `  `/* Utility function to print a linked list */` `static` `void` `printList(Node head)  ` `{  ` `    ``while` `(head != ``null``)  ` `    ``{  ` `        ``Console.Write(head.data + ``" "``);  ` `        ``head = head.next;  ` `    ``}  ` `    ``Console.WriteLine();  ` `}  ` ` `  `// Driver Code ` `public` `static` `void` `Main(String[] args)  ` `{ ` `    ``head = ``null``;  ` ` `  `    ``/* Create following linked list  ` `    ``12.15.10.11.5.6.2.3 */` `    ``push(head, 3);  ` `    ``push(head, 2);  ` `    ``push(head, 6);  ` `    ``push(head, 5);  ` `    ``push(head, 11);  ` `    ``push(head, 10);  ` `    ``push(head, 15);  ` `    ``push(head, 12);  ` ` `  `    ``Console.WriteLine(``"Given Linked List"``);  ` `    ``printList(head);  ` `    ``max = ``int``.MinValue;  ` `    ``head = delNodes(head);  ` ` `  `    ``Console.WriteLine(``"Modified Linked List"``);  ` `    ``printList(head); ` `} ` `} ` ` `  `// This code is contributed by PrinciRaj1992 `

Output:

```Given Linked List
12 15 10 11 5 6 2 3
15 11 6 3
```

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