C++ Program For Removing Middle Points From a Linked List Of Line Segments

// C++ program to remove intermediate points
// in a linked list that represents horizontal
// and vertical line segments 
#include <bits/stdc++.h>
using namespace std; 

// Node has 3 fields including x, y 
// coordinates and a pointer 
// to next node 
class Node 
{ 
    public:
    int x, y; 
    Node *next; 
}; 

/* Function to insert a node 
   at the beginning */
void push(Node ** head_ref, 
          int x,int y) 
{ 
    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(Node *head) 
{ 
    Node *temp = head; 
    while (temp != NULL) 
    { 
        cout << "(" << temp->x << 
                "," << temp->y << ")-> "; 
        temp = temp->next; 
    } 
    cout << endl;
} 

// Utility function to remove Next 
// from linked list and link nodes 
// after it to head 
void deleteNode(Node *head, 
                Node *Next) 
{ 
    head->next = Next->next; 
    Next->next = NULL; 
    free(Next); 
} 

// This function deletes middle nodes 
// in a sequence of horizontal and 
// vertical line segments represented 
// by linked list. 
Node* deleteMiddle(Node *head) 
{ 
    // 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 a vertical line 
    // or horizontal line 
    if (head->x == Next->x) 
    { 
        // Find middle nodes with same x 
        // value, and delete them 
        while (NextNext != NULL && 
               Next->x == NextNext->x) 
        { 
            deleteNode(head, Next); 

            // Update Next and NextNext 
            // for next iteration 
            Next = NextNext; 
            NextNext = NextNext->next; 
        } 
    } 

    // If horizontal line 
    else if (head->y == Next->y) 
    { 
        // Find middle nodes with same y 
        // value, and delete them 
        while (NextNext != NULL && 
               Next->y == NextNext->y) 
        { 
            deleteNode(head, Next); 

            // Update Next and NextNext for 
            // next iteration 
            Next = NextNext; 
            NextNext = NextNext->next; 
        } 
    } 

    // Adjacent points must have either 
    // same x or same y 
    else 
    { 
        puts("Given linked list is not valid"); 
        return NULL; 
    } 

    // Recur for next segment 
    deleteMiddle(head->next); 

    return head; 
} 

// Driver code
int main() 
{ 
    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); 
    cout << "Given Linked List: "; 
    printList(head); 

    if (deleteMiddle(head) != NULL); 
    { 
        cout << "Modified Linked List: "; 
        printList(head); 
    } 
    return 0; 
} 
// This is code is contributed by rathbhupendra