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len_loop_linked_list.cpp
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len_loop_linked_list.cpp
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#include<bits/stdc++.h>
using namespace std;
/* Link list node */
struct Node
{
int data;
struct Node* next;
};
// Returns count of nodes present in loop.
int countNodes(struct Node *n)
{
int res = 1;
struct Node *temp = n;
while (temp->next != n)
{
res++;
temp = temp->next;
}
return res;
}
/* This function detects and counts loop
nodes in the list. If loop is not there
in then returns 0 */
int countNodesinLoop(struct Node *list)
{
struct Node *slow_p = list, *fast_p = list;
while (slow_p && fast_p &&
fast_p->next)
{
slow_p = slow_p->next;
fast_p = fast_p->next->next;
/* If slow_p and fast_p meet at
some point then there is a loop */
if (slow_p == fast_p)
return countNodes(slow_p);
}
/* Return 0 to indeciate that
their is no loop*/
return 0;
}
struct Node *newNode(int key)
{
struct Node *temp =
(struct Node*)malloc(sizeof(struct Node));
temp->data = key;
temp->next = NULL;
return temp;
}
// Driver Code
int main()
{
struct Node *head = newNode(1);
head->next = newNode(2);
head->next->next = newNode(3);
head->next->next->next = newNode(4);
head->next->next->next->next = newNode(5);
/* Create a loop for testing */
head->next->next->next->next->next = head->next;
cout << countNodesinLoop(head) << endl;
return 0;
}