Question

How to check if a linked list is circular linked list in C++

Answer 1

#include <bits/stdc++.h> 

using namespace std; 
  
struct Node { 
    int n; 
    struct Node* next; 
}; 
  
bool isCircular(struct Node *head) { 
    if (head == NULL) 
       return true; 
  
    struct Node *nodeNext = head->next; 
  
    while (nodeNext != NULL && nodeNext != head) 
       nodeNext = nodeNext->next; 
  
    return (nodeNext == head); 
} 
  
Node *addNewNode(int data) { 
    struct Node *newNode = new Node;
    
    newNode->n = data; 
    newNode->next = NULL; 
    
    return newNode; 
} 

void deleteLinkedList(struct Node *head) {
    struct Node *next;
    while (head != NULL)  {  
        next = head->next;  
        free(head);  
        head = next;  
    }  
}
  
int main() 
{ 
    struct Node* head = addNewNode(1); 
    
    head->next = addNewNode(2); 
    head->next->next = addNewNode(3); 

  
    isCircular(head)? cout << "Yes\n" :  cout << "No\n" ; 
  
    head->next->next->next = addNewNode(4); 
    head->next->next->next->next = head; 
  
    isCircular(head)? cout << "Yes\n" : cout << "No\n" ; 
    
    head->next->next->next->next = NULL;
    
    isCircular(head)? cout << "Yes\n" : cout << "No\n" ; 
    
    deleteLinkedList(head);
  
    return 0; 
} 



/*
run:

No
Yes
No

*/

 

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