Determine whether a one-way linked list has loops and

Determine whether a one-way linked list has loops and

1. Set up two pointers, I, and j points to the header node.

2. I take step 1 and step j. If there is a ring, j will surely catch up with I;

3. If j is not empty and I and j are equal, this linked list is a ring.

 

1 # include <stdio. h> 2 # include <stdlib. h> 3 # include <string. h> 4 typedef struct student // define the chain table structure 5 {6 int num; 7 struct student * pnext; 8} stu, * pstu; 9 void link_tail_insert (pstu * phead, pstu * ptail, int I); 10 void link_show (pstu); 11 void link_judge_loop (pstu phead); 12 void main () {13 pstu phead, ptail; 14 int I; 15 phead = NULL; 16 ptail = NULL; 17 while (scanf ("% d", & I )! = EOF) {18 link_tail_insert (& phead, & ptail, I); 19} 20 link_show (phead); 21 ptail-> pnext = phead; // create a single-chain table with 22 link_judge_loop (phead); 23 system ("pause"); 24 25} 26 void link_tail_insert (pstu * phead, pstu * ptail, int I) {// create a chain table 27 pstu pnew; 28 pnew = (pstu) malloc (sizeof (stu); 29 memset (pnew, 0, sizeof (stu )); 30 pnew-> num = I; 31 if (* ptail = NULL) {32 * phead = pnew; 33 * ptail = pnew; 34} 35 else {36 (* ptail)-> pnext = pnew; 37 * ptail = pnew; 38} 39} 40 void link_show (pstu phead) {// output chain table 41 pstu pshow; 42 pshow = phead; 43 if (phead = NULL) 44 {45 printf ("no exsit \ n"); 46 return; 47} 48 while (pshow! = NULL) {49 printf ("% d", pshow-> num); 50 pshow = pshow-> pnext; 51} 52 putchar ('\ n '); 53} 54 void link_judge_loop (pstu phead) {// determine whether there is a ring 55 pstu I, j; 56 I = j = phead; 57 while (j! = NULL) {58 I = I-> pnext; 59 j = j-> pnext; 60 if (j = NULL) // j should be taken step by step to determine whether it is NULL, if it is null, the end loop 61 break; 62 j = j-> pnext; 63 if (I = j) // I and j are equal, with a ring of 64 break; 65} 66 if (j! = NULL & I = j) 67 printf ("link has loop \ n"); 68 else 69 printf ("link has no loop \ n"); 70}