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× C++ Data Structures - Linked List Other Related Topics


Deleting even nodes of a linked list requires traverse through the list and deleting even nodes one by one. It requires creating two nodes - oddNode and evenNode. If head is not null, make oddNode to first odd node of list and evenNode to first even node of the list. If both are not null, delete the evenNode and adjust links. Move both nodes to next set of odd-even nodes. Repeat the process till any or both nodes become null.

The function deleteEvenNodes is created for this purpose. It is a 4-step process.

void deleteEvenNodes() {
  if(head != NULL) {
  
    //1. if head is not null create nodes -
    //   evenNode and oddNode
    Node* oddNode = head;
    Node* evenNode = head->next; 

    while(oddNode != NULL && evenNode != NULL) {
      
      //2. while oddNode and evenNode are not null
      //   make next of oddNode as next of evenNode 
      //   and free evenNode   
      oddNode->next = evenNode->next;
      free(evenNode);

      //3. and make oddNode as next of oddNode
      oddNode = oddNode->next;
      
      //4. Update oddNode and evenNode
      if(oddNode != NULL)
        evenNode = oddNode->next;
    }
  }
} 

The below is a complete program that uses above discussed concept of deleting even nodes of a linked list.

#include <iostream>
using namespace std;

//node structure
struct Node {
    int data;
    Node* next;
};

class LinkedList {
  private:
    Node* head;
  public:
    LinkedList(){
      head = NULL;
    }
 
    //Add new element at the end of the list
    void push_back(int newElement) {
      Node* newNode = new Node();
      newNode->data = newElement;
      newNode->next = NULL; 
      if(head == NULL) {
        head = newNode;
      } else {
        Node* temp = head;
        while(temp->next != NULL)
          temp = temp->next;
        temp->next = newNode;
      }    
    }
    
    //delete even nodes of the list
    void deleteEvenNodes() {
      if(head != NULL) {
        Node* oddNode = head;
        Node* evenNode = head->next; 
        while(oddNode != NULL && evenNode != NULL) {
          oddNode->next = evenNode->next;
          free(evenNode);
          oddNode = oddNode->next;
          if(oddNode != NULL)
            evenNode = oddNode->next;
        }
      }
    } 

    //display the content of the list
    void PrintList() {
      Node* temp = head;
      if(temp != NULL) {
        cout<<"\nThe list contains: ";
        while(temp != NULL) {
          cout<<temp->data<<" ";
          temp = temp->next;
        }
      } else {
        cout<<"\nThe list is empty.";
      }
    }    
};

// test the code 
int main() {
  LinkedList MyList;

  //Add five elements in the list.
  MyList.push_back(10);
  MyList.push_back(20);
  MyList.push_back(30);
  MyList.push_back(40);
  MyList.push_back(50);

  //Display the content of the list.
  MyList.PrintList();

  //delete even nodes of the list
  MyList.deleteEvenNodes();

  cout<<"\nAfter deleting even nodes.";
  //Display the content of the list.
  MyList.PrintList();
  
  return 0; 
}

The above code will give the following output:

The list contains: 10 20 30 40 50 
After deleting even nodes.
The list contains: 10 30 50