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Iterative approach for removing middle points in a linked list of line segements

This post explains the iterative approach of this problem.
We maintain two pointers, prev and temp. If these two have either x or y same, we move forward till the equality holds and keep deleting the nodes in between. The node from which the equality started, we adjust the next pointer of that node.

C++

// C++ program to remove intermediate  
// points in a linked list that represents 
// horizontal and vertical line segments 
#include <iostream> 
using namespace std; 
  
// Node has 3 fields including x, y 
// coordinates and a pointer to next node 
struct Node { 
    int x, y; 
    struct Node *next; 
}; 
  
/* Function to insert a node at the beginning */
void push(struct Node **head_ref, int x, int y) 
{ 
    struct Node *new_node = new Node;    
    new_node->x = x; 
    new_node->y = y; 
    new_node->next = (*head_ref); 
    (*head_ref) = new_node; 
} 
  
/* Utility function to print a singly linked list */
void printList(struct Node *head) 
{ 
    struct Node *temp = head;     
    while (temp != NULL) { 
        printf("(%d, %d)-> ", temp->x, temp->y);         
        temp = temp->next; 
    }     
    printf("\n"); 
} 
  
// This function deletes middle nodes in a  
// sequence of horizontal and vertical line  
// segments represented by linked list. 
void delete_Middle_Nodes(Node *head)  
{     
    Node *temp = head->next, *prev = head;   
    
    while (temp) { 
          
        // checking equlity of point x 
        if (temp->x == prev->x)  
        { 
            Node *curr = prev; 
            prev = temp; 
            temp = temp->next;         
              
            // removing vertical points of line  
            // segment from linked list 
            while (temp && temp->x == prev->x)  
            { 
                curr->next = temp; 
                free(prev); 
                prev = temp; 
                temp = temp->next; 
            } 
        } 
  
        // checking equlity of point y 
        else if (temp->y == prev->y)  
        { 
            Node *curr = prev; 
            prev = temp; 
            temp = temp->next; 
              
            // removing horizontal points of line  
            // segment from linked list 
            while (temp && temp->y == prev->y) 
            { 
                curr->next = temp; 
                free(prev); 
                prev = temp; 
                temp = temp->next; 
            } 
        } else { 
            prev = temp; 
            temp = temp->next; 
        } 
    } 
} 
  
// Driver program to test above functions 
int main() { 
    struct Node *head = NULL; 
      
    push(&head, 40,5); 
    push(&head, 20,5); 
    push(&head, 10,5); 
    push(&head, 10,8); 
    push(&head, 10,10); 
    push(&head, 3,10); 
    push(&head, 1,10); 
    push(&head, 0,10); 
      
    printf("Given Linked List: \n"); 
    printList(head); 
      
    delete_Middle_Nodes(head); 
      
    printf("Modified Linked List: \n"); 
    printList(head); 
      
    return 0; 
} 

Java

class LinkedList 
{ 
    Node head; // head of list 
  
    /* 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. 
    private void delete_Middle_Nodes(Node head) 
    { 
        Node prev = head; 
        Node temp = head.next; 
  
        while (temp != null) 
        { 
  
            // checking equlity of point x 
            if (temp.x == prev.x) 
            { 
                Node curr = prev; 
                prev = temp; 
                temp = temp.next; 
  
                // removing vertical points of line  
                // segment from linked list 
                while (temp != null && temp.x == prev.x) 
                { 
                    curr.next = temp; 
                    prev.next = null; 
                    prev = temp; 
                    temp = temp.next; 
                } 
            } 
  
            // checking equlity of point y  
            else if (temp.y == prev.y) 
            { 
                Node curr = prev; 
                prev = temp; 
                temp = temp.next; 
  
                // removing horizontal points of line  
                // segment from linked list 
                while (temp != null && temp.y == prev.y) 
                { 
                    curr.next = temp; 
                    prev.next = null; 
                    prev = temp; 
                    temp = temp.next; 
                } 
            }  
            else
            { 
                prev =temp; 
                temp = temp.next; 
            } 
        } 
    } 
  
    /* 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 code */
    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(); 
  
        llist.delete_Middle_Nodes(llist.head); 
  
        System.out.println("Modified Linked List is"); 
        llist.printList(); 
    } 
} 
  
// This code is contributed by shubham96301. 

Python3

# Python3 program to remove intermediate  
# points in a linked list that represents 
# horizontal and vertical line segments 
import math 
  
# Node has 3 fields including x, y 
# coordinates and a pointer to next node 
class Node:  
    def __init__(self, x, y):  
        self.x = x 
        self.y = y 
        self.next = None
  
# Function to insert a node at the beginning  
def push(head_ref, x, y): 
    new_node = Node(x, y)  
    new_node.x = x 
    new_node.y = y 
    new_node.next = head_ref 
    head_ref = new_node 
    return head_ref 
  
# Utility function to print  
# a singly linked list  
def printList(head): 
    temp = head  
    while (temp != None): 
        print("(", temp.x, ",", 
                   temp.y, ")", end = "->",)      
        temp = temp.next
          
    print() 
  
# This function deletes middle nodes in a  
# sequence of horizontal and vertical line  
# segments represented by linked list. 
def delete_Middle_Nodes(head):  
    temp = head.next
    prev = head  
      
    while (temp): 
          
        # checking equlity of point x 
        if (temp.x == prev.x): 
            curr = prev 
            prev = temp 
            temp = temp.next    
              
            # removing vertical points of line  
            # segment from linked list 
            while (temp != None and temp.x == prev.x): 
                curr.next = temp 
                  
                #free(prev) 
                prev = temp 
                temp = temp.next
              
        # checking equlity of point y 
        elif (temp.y == prev.y): 
            curr = prev 
            prev = temp 
            temp = temp.next
              
            # removing horizontal points of line  
            # segment from linked list 
            while (temp != None and temp.y == prev.y): 
                curr.next = temp 
                #free(prev) 
                prev = temp 
                temp = temp.next
              
        else: 
            prev = temp 
            temp = temp.next
          
# Driver Code 
if __name__=='__main__':  
    head = None
      
    head = push(head, 40, 5) 
    head = push(head, 20, 5) 
    head = push(head, 10, 5) 
    head = push(head, 10, 8) 
    head = push(head, 10, 10) 
    head = push(head, 3, 10) 
    head = push(head, 1, 10) 
    head = push(head, 0, 10) 
      
    print("Given Linked List: \n", end = "") 
    printList(head) 
      
    delete_Middle_Nodes(head) 
      
    print("Modified Linked List: \n", end = "") 
    printList(head) 
      
# This code is contributed by AbhiThakur 

C#

// C# program to remove intermediate  
// points in a linked list that represents 
// horizontal and vertical line segments 
using System; 
      
public class LinkedList 
{ 
    public Node head; // head of list 
  
    /* Linked list Node*/
    public class Node 
    { 
        public int x,y; 
        public Node next; 
        public 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. 
    private void delete_Middle_Nodes(Node head) 
    { 
        Node prev = head; 
        Node temp = head.next; 
  
        while (temp != null) 
        { 
  
            // checking equlity of point x 
            if (temp.x == prev.x) 
            { 
                Node curr = prev; 
                prev = temp; 
                temp = temp.next; 
  
                // removing vertical points of line  
                // segment from linked list 
                while (temp != null && temp.x == prev.x) 
                { 
                    curr.next = temp; 
                    prev.next = null; 
                    prev = temp; 
                    temp = temp.next; 
                } 
            } 
  
            // checking equlity of point y  
            else if (temp.y == prev.y) 
            { 
                Node curr = prev; 
                prev = temp; 
                temp = temp.next; 
  
                // removing horizontal points of line  
                // segment from linked list 
                while (temp != null && temp.y == prev.y) 
                { 
                    curr.next = temp; 
                    prev.next = null; 
                    prev = temp; 
                    temp = temp.next; 
                } 
            }  
            else
            { 
                prev =temp; 
                temp = temp.next; 
            } 
        } 
    } 
  
    /* 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) 
        { 
            Console.Write("(" + temp.x + "," + temp.y + ")->"); 
            temp = temp.next; 
        } 
        Console.WriteLine(); 
    } 
  
  
    /* Driver code */
    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); 
  
        Console.WriteLine("Given list"); 
        llist.printList(); 
  
        llist.delete_Middle_Nodes(llist.head); 
  
        Console.WriteLine("Modified Linked List is"); 
        llist.printList(); 
    } 
} 
  
/* This code contributed by PrinciRaj1992 */

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)->

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