Two ways to determine whether a single-linked list has a ring

Source: Internet
Author: User

, if the single-linked list has a ring, then when traversing, after passing 6, will be back to 3, then we can use two pointers during the traversal to see whether two pointers are equal.

Method One: Use P, q Two pointers, p always go forward, but Q every time to start from the beginning, for each node, see p Walk step number is the same as Q. , when p from 6 to 3 o'clock, with 6 steps, at this time if Q from head, then only two steps to 3, thus varying the number of steps, there are contradictions, the existence of the ring
Method Two: Use P, q two pointers, p each step forward, Q each forward two steps, if at some point p = = Q, there is a ring.

#include <stdio.h>#include<stdlib.h>#defineLEN 8typedefstructnode*node_t;structnode{CharVal; structNode *Next;  }; //Method 1intHas_loop (structNode *head);//Method 2intHas_loop2 (node_t head);intMain () {node_t* arr = (node_t*)malloc(sizeof(structnode) *LEN); arr[0] = (node_t)malloc(sizeof(structnode)); inti;  for(i =1; i < LEN; i++) {Arr[i]= (node_t)malloc(sizeof(structnode)); Arr[i-1]->next =Arr[i]; } Arr[len-1]->next =NULL; //You can add a loop here to test//arr[6]->next = arr[0];    if(Has_loop (arr[0]) printf ("Method1:has loop.\n"); Elseprintf ("Method1:has No loop.\n"); if(Has_loop2 (arr[0]) printf ("Method2:has loop.\n"); Elseprintf ("Method2:has No loop.\n"); return 0;}//If the pointer is equal, but they don't have the same steps and then has a loopintHas_loop (node_t head) {node_t Cur1=Head; intPOS1 =0;  while(cur1) {node_t cur2=Head; intPos2 =0; POS1++;  while(CUR2) {Pos2++; if(CUR2 = =cur1) {                  if(POS1 = =Pos2) Break; Else                      return 1; } CUR2= cur2->Next; } cur1= cur1->Next; }      return 0; } //using Step1 and Step2 here//if exists a loop, then the pointer which use Step2 'll catch up with the pointer which uses STEP1intHas_loop2 (node_t head) {node_t P=Head; node_t Q=Head;  while(P! = NULL && Q! =NULL) {        /*p = p->next;        if (q->next! = NULL) Q = q->next->next;            if (p = = q) return 1; */        //correct it on 17/11/2012p = p->Next; Q= q->Next; if(Q! =NULL) Q= q->Next; if(P! = NULL && p = =q)return 1; }    return 0;}


Translated from http://www.cnblogs.com/shuaiwhu/archive/2012/05/03/2480509.html

Two methods of judging whether a single linked list has a ring (turn)

Contact Us

The content source of this page is from Internet, which doesn't represent Alibaba Cloud's opinion; products and services mentioned on that page don't have any relationship with Alibaba Cloud. If the content of the page makes you feel confusing, please write us an email, we will handle the problem within 5 days after receiving your email.

If you find any instances of plagiarism from the community, please send an email to: info-contact@alibabacloud.com and provide relevant evidence. A staff member will contact you within 5 working days.

A Free Trial That Lets You Build Big!

Start building with 50+ products and up to 12 months usage for Elastic Compute Service

  • Sales Support

    1 on 1 presale consultation

  • After-Sales Support

    24/7 Technical Support 6 Free Tickets per Quarter Faster Response

  • Alibaba Cloud offers highly flexible support services tailored to meet your exact needs.