How to determine whether a linked list has a loop

1, the link is to determine whether there is a loop?

(1) Loop definition:

1-2-3-4-5-6-7

| |

----8

As in the case above, it means that there is a loop.

(2) solve the idea:

Description: Use the speed pointer, the slow pointer each time only before further, the quick pointer each step forward two steps, until the slow pointer meets the quick pointer.

2, paste the code

(1) Definition of data structure

#ifndef linklist_h
#define LINKLIST_H
   
#define NULL 0
   
typedef struct MYNODE
{
    int data;
    struct mynode* next;

#endif

(2) Judge the function Isexistlookbackup (Mynode *node), return True if it exists, or false.

1 #ifndef linklist_back_h

#define LINKLIST_BACK_H
#include "LinkedList.h"
bool Isexistlookbackup (mynode* node)
{
    if (node = = NULL | | Node->next = = NULL) return
        false;
    mynode*-node;
    mynode* second = node->next->next;
    while (true)
    {
        if (second = null | | | second->next = NULL) break
            ;
        if (A/= second) return
            true;
        first=first->next;
        Second = second->next->next;
    }
    return false;        
}
   
#endif//! Linklist_h