Java Program For Removing Middle Points From a Linked List Of Line Segments
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.
Source: Microsoft Interview Experience
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
// 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)-> Modified Linked List: (0,10)-> (10,10)-> (10,5)-> (40,5)->
Time Complexity of the above solution is O(n) where n is a number of nodes in the given linked list.
Auxiliary Space: O(1) because it is using constant space
Exercise:
The above code is recursive, write an iterative code for the same problem. Please see below for the solution.
Iterative approach for removing middle points in a linked list of line segments Please refer complete article on Given a linked list of line segments, remove middle points for more details!
