# Java Program To Delete Nodes Which Have A Greater Value On Right Side

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

Examples:

```Input: 12->15->10->11->5->6->2->3->NULL
Output: 15->11->6->3->NULL
Explanation: 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

Input: 10->20->30->40->50->60->NULL
Output: 60->NULL
Explanation: 10, 20, 30, 40, and 50 have been deleted because
they all have a greater value on the right side.

Input: 60->50->40->30->20->10->NULL
Output: No Change.```

Method 1 (Simple):
Use two loops. In the outer loop, pick nodes of the linked list one by one. In the inner loop, check if there exists a node whose value is greater than the picked node. If there exists a node whose value is greater, then delete the picked node.
Time Complexity: O(n^2)

Method 2 (Use Reverse):
Thanks to Paras for providing the below algorithm.
1. Reverse the list.
2. Traverse the reversed list. Keep max till now. If the next node is less than max, then delete the next node, otherwise max = next node.
3. Reverse the list again to retain the original order.
Time Complexity: O(n)
Thanks to R.Srinivasan for providing the code below.

## Java

 `// Java program to delete nodes which have ` `// a greater value on right side` `class` `LinkedList ` `{` `    ``// head of list` `    ``Node head; `   `    ``// Linked list Node` `    ``class` `Node ` `    ``{` `        ``int` `data;` `        ``Node next;` `        ``Node(``int` `d)` `        ``{` `            ``data = d;` `            ``next = ``null``;` `        ``}` `    ``}`   `    ``/* Deletes nodes which have a node ` `       ``with greater value node on left side */` `    ``void` `delLesserNodes()` `    ``{` `        ``// 1.Reverse the linked list ` `        ``reverseList();`   `        ``/* 2. In the reversed list, delete nodes ` `              ``which have a node with greater value ` `              ``node on left side. Note that head node ` `              ``is never deleted because it is the ` `              ``leftmost node.*/` `        ``_delLesserNodes();`   `        ``/* 3. Reverse the linked list again to retain` `              ``the original order */` `        ``reverseList();` `    ``}`   `    ``/* Deletes nodes which have greater value ` `       ``node(s) on left side */` `    ``void` `_delLesserNodes()` `    ``{` `        ``Node current = head;`   `        ``// Initialise max ` `        ``Node maxnode = head;` `        ``Node temp;`   `        ``while` `(current != ``null` `&& ` `               ``current.next != ``null``) ` `        ``{` `            ``/* If current is smaller than max, ` `               ``then delete current */` `            ``if` `(current.next.data < maxnode.data) ` `            ``{` `                ``temp = current.next;` `                ``current.next = temp.next;` `                ``temp = ``null``;` `            ``}`   `            ``/* If current is greater than max, ` `               ``then update max and move current */` `            ``else` `            ``{` `                ``current = current.next;` `                ``maxnode = current;` `            ``}` `        ``}` `    ``}`   `    ``// Utility functions ` `    ``/* Inserts a new Node at front of ` `       ``the list. */` `    ``void` `push(``int` `new_data)` `    ``{` `        ``/* 1 & 2: Allocate the Node &` `                  ``Put in the data*/` `        ``Node new_node = ``new` `Node(new_data);`   `        ``// 3. Make next of new Node as head ` `        ``new_node.next = head;`   `        ``// 4. Move the head to point to ` `        ``// new Node ` `        ``head = new_node;` `    ``}`   `    ``// Function to reverse the linked list ` `    ``void` `reverseList()` `    ``{` `        ``Node current = head;` `        ``Node prev = ``null``;` `        ``Node next;` `        ``while` `(current != ``null``) ` `        ``{` `            ``next = current.next;` `            ``current.next = prev;` `            ``prev = current;` `            ``current = next;` `        ``}` `        ``head = prev;` `    ``}`   `    ``// Function to print linked list ` `    ``void` `printList()` `    ``{` `        ``Node temp = head;` `        ``while` `(temp != ``null``) ` `        ``{` `            ``System.out.print(temp.data + ` `                             ``" "``);` `            ``temp = temp.next;` `        ``}` `        ``System.out.println();` `    ``}`   `    ``// Driver code` `    ``public` `static` `void` `main(String args[])` `    ``{` `        ``LinkedList llist = ``new` `LinkedList();`   `        ``/* Constructed Linked List is ` `           ``12->15->10->11->5->6->2->3 */` `        ``llist.push(``3``);` `        ``llist.push(``2``);` `        ``llist.push(``6``);` `        ``llist.push(``5``);` `        ``llist.push(``11``);` `        ``llist.push(``10``);` `        ``llist.push(``15``);` `        ``llist.push(``12``);`   `        ``System.out.println(``"Given Linked List"``);` `        ``llist.printList();`   `        ``llist.delLesserNodes();`   `        ``System.out.println(``"Modified Linked List"``);` `        ``llist.printList();` `    ``}` `} ` `// This code is contributed by Rajat Mishra `

Output:

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

Time Complexity: O(n)

Auxiliary Space: O(1)

Method 3: The other simpler method is to traverse the list from the start and delete the node when the current Node < next Node. To delete the current node, follow this approach. Let us assume you have to delete current node X:

1. Copy next node’s data into X i.e X.data = X.next.data.
2. Copy next node’s next address i.e X.next = X.next.next.

Move forward in the List only when the current Node is > the next Node.

## Java

 `// Java program for above approach` `import` `java.io.*;`   `// This class represents a single node ` `// in a linked list` `class` `Node ` `{    ` `    ``int` `data;` `    ``Node next;` `    `  `    ``public` `Node(``int` `data)` `    ``{` `        ``this``.data = data;` `        ``this``.next = ``null``;` `    ``}` `}`   `//This is a utility class for ` `// linked list` `class` `LLUtil` `{    ` `    ``// This function creates a linked list ` `    ``// from a given array and returns head` `    ``public` `Node createLL(``int``[] arr)` `    ``{        ` `        ``Node head = ``new` `Node(arr[``0``]);` `        ``Node temp = head;` `        `  `        ``Node newNode = ``null``;` `        ``for``(``int` `i = ``1``; i < arr.length; i++)` `        ``{` `            ``newNode = ``new` `Node(arr[i]);` `            ``temp.next = newNode;` `            ``temp = temp.next;` `        ``}` `        ``return` `head;` `    ``}` `  `  `      ``// This function prints given ` `      ``// linked list` `      ``public` `void` `printLL(Node head)` `      ``{        ` `        ``while``(head != ``null``)` `        ``{` `            ``System.out.print(head.data +` `                             ``" "``);` `            ``head = head.next;` `        ``}` `        ``System.out.println();` `    ``}  ` `}`   `// Driver code` `class` `GFG ` `{` `    ``public` `static` `void` `main (String[] args) ` `    ``{        ` `        ``int``[] arr = {``12``, ``15``, ``10``, ``11``, ` `                     ``5``, ``6``, ``2``, ``3``};` `        ``LLUtil llu = ``new` `LLUtil();` `        ``Node head = llu.createLL(arr);` `        ``System.out.println(``"Given Linked List"``);` `        ``llu.printLL(head);` `        ``head = deleteNodesOnRightSide(head);` `        ``System.out.println(``"Modified Linked List"``);` `        ``llu.printLL(head);` `          `  `    ``}` `    `  `    ``//Main function` `    ``public` `static` `Node deleteNodesOnRightSide(Node head)` `    ``{` `         ``if``(head == ``null` `|| head.next == ``null``) ` `             ``return` `head;`   `         ``Node nextNode = deleteNodesOnRightSide(head.next);`   `         ``if``(nextNode.data > head.data) ` `             ``return` `nextNode;` `         ``head.next = nextNode;`   `         ``return` `head;` `    ``}` `}`

Output:

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