Data Structure Linked List: Detect and Remove Loop in a Linked List

http://www.geeksforgeeks.org/detect-and-remove-loop-in-a-linked-list/

 1 #include <iostream>

 2 #include <vector>

 3 #include <algorithm>

 4 #include <queue>

 5 #include <stack>

 6 #include <string>

 7 #include <fstream>

 8 #include <map>

 9 #include <set>

10 using namespace std;

11 

12 struct node {

13     int data;

14     node *next;

15     node() : data(0), next(NULL) { }

16     node(int d) : data(d), next(NULL) { }

17 };

18 

19 void push(node* &head, int k) {

20     node *new_node = new node(k);

21     new_node->next = head;

22     head = new_node;

23 }

24 

25 void detectandremove(node *&head) {

26     node *p, *q;

27     p = q = head;

28     while (q && q->next) {

29         q = q->next->next;

30         p = p->next;

31         if (p == q) break;

32     }

33     if (!q || !q->next) return; //no loop

34     q = head;

35     while (q != p) {

36         q = q->next;

37         p = p->next;

38     } //get the starting point of the ring

39     while (q->next != p) q = q->next; //get the point before the starting point of the ring

40     q->next = NULL; //remove the ring

41 }

42 

43 void print(node *head) {

44     while (head) {

45         cout << head->data << " ";

46         head = head->next;

47     }

48 }

49 

50 int main() {

51     node *head = NULL;

52     push(head, 10);

53     push(head, 4);

54     push(head, 15);

55     push(head, 20);

56     push(head, 50);

57     push(head, 60);

58     head->next->next->next->next->next->next = head->next->next->next;

59     detectandremove(head);

60     print(head);

61     return 0;

62 }