# Java Program For Removing Middle Points From a Linked List Of Line Segments

• Last Updated : 27 Dec, 2021

Given a linked list of coordinates where adjacent points either form a vertical line or a horizontal line. Delete points from the linked list which are in the middle of a horizontal or vertical line.
Examples:

```Input:   (0,10)->(1,10)->(5,10)->(7,10)
|
(7,5)->(20,5)->(40,5)
Output: Linked List should be changed to following
(0,10)->(7,10)
|
(7,5)->(40,5)
The given linked list represents a horizontal line from (0,10)
to (7, 10) followed by a vertical line from (7, 10) to (7, 5),
followed by a horizontal line from (7, 5) to (40, 5).

Input: (2,3)->(4,3)->(6,3)->(10,3)->(12,3)
Output: Linked List should be changed to following
(2,3)->(12,3)
There is only one vertical line, so all middle points are removed.```

The idea is to keep track of the current node, next node, and next-next node. While the next node is the same as the next-next node, keep deleting the next node. In this complete procedure, we need to keep an eye on the shifting of pointers and checking for NULL values.
Following are implementations of the above idea.

## Java

 `// Java program to remove middle points in ``// a linked list of line segments,``class` `LinkedList``{``    ``// Head of list``    ``Node head;  `` ` `    ``// Linked list Node``    ``class` `Node``    ``{``        ``int` `x,y;``        ``Node next;``        ``Node(``int` `x, ``int` `y)``        ``{``            ``this``.x = x;``            ``this``.y = y;``            ``next = ``null``;``        ``}``    ``}`` ` `    ``// This function deletes middle nodes ``    ``// in a sequence of horizontal and``    ``// vertical line segments represented``    ``// by linked list.``    ``Node deleteMiddle()``    ``{``        ``// If only one node or no node...``        ``// Return back``        ``if` `(head == ``null` `|| ``            ``head.next == ``null` `||``            ``head.next.next == ``null``)``            ``return` `head;`` ` `        ``Node Next = head.next;``        ``Node NextNext = Next.next;`` ` `        ``// Check if this is vertical or ``        ``// horizontal line``        ``if` `(head.x == Next.x)``        ``{``            ``// Find middle nodes with same value ``            ``// as x and delete them.``            ``while` `(NextNext != ``null` `&& ``                   ``Next.x == NextNext.x)``            ``{``                ``head.next = Next.next;``                ``Next.next = ``null``;`` ` `                ``// Update NextNext for the next iteration``                ``Next = NextNext;``                ``NextNext = NextNext.next;``            ``}``        ``}`` ` `        ``// if horizontal``        ``else` `if` `(head.y == Next.y)``        ``{``            ``// find middle nodes with same value as y and``            ``// delete them``            ``while` `(NextNext != ``null` `&& Next.y == NextNext.y)``            ``{``                ``head.next = Next.next;``                ``Next.next = ``null``;`` ` `                ``// Update NextNext for the next iteration``                ``Next = NextNext;``                ``NextNext = NextNext.next;``            ``}``        ``}`` ` `        ``// Adjacent points should have same x or same y``        ``else``        ``{``            ``System.out.println(``"Given list is not valid"``);``            ``return` `null``;``        ``}`` ` `        ``// recur for other segment`` ` `        ``// temporarily store the head and move head forward.``        ``Node temp = head;``        ``head = head.next;`` ` `        ``// call deleteMiddle() for next segment``        ``this``.deleteMiddle();`` ` `        ``// restore head``        ``head = temp;`` ` `        ``// return the head``        ``return` `head;``    ``}`` ` `    ``/*  Given a reference (pointer to pointer) to the head``        ``of a list and an int, push a new node on the front``        ``of the list. */``    ``void` `push(``int` `x, ``int` `y)``    ``{``        ``/* 1 & 2: Allocate the Node &``                  ``Put in the data*/``        ``Node new_node = ``new` `Node(x,y);`` ` `        ``/* 3. Make next of new Node as head */``        ``new_node.next = head;`` ` `        ``/* 4. Move the head to point to new Node */``        ``head = new_node;``    ``}`` ` ` ` `    ``void` `printList()``    ``{``        ``Node temp = head;``        ``while` `(temp != ``null``)``        ``{``            ``System.out.print(``"("``+temp.x+``","``+temp.y+``")->"``);``            ``temp = temp.next;``        ``}``        ``System.out.println();``    ``}`` ` ` ` `    ``/* Driver program to test above functions */``    ``public` `static` `void` `main(String args[])``    ``{``        ``LinkedList llist = ``new` `LinkedList();`` ` `        ``llist.push(``40``,``5``);``        ``llist.push(``20``,``5``);``        ``llist.push(``10``,``5``);``        ``llist.push(``10``,``8``);``        ``llist.push(``10``,``10``);``        ``llist.push(``3``,``10``);``        ``llist.push(``1``,``10``);``        ``llist.push(``0``,``10``);`` ` `        ``System.out.println(``"Given list"``);``        ``llist.printList();`` ` `        ``if` `(llist.deleteMiddle() != ``null``)``        ``{``            ``System.out.println(``"Modified Linked List is"``);``            ``llist.printList();``        ``}``    ``}``} ``/* This code is contributed by Rajat Mishra */`

Output:

```Given Linked List:
(0,10)-> (1,10)-> (3,10)-> (10,10)-> (10,8)-> (10,5)-> (20,5)-> (40,5)->