 ronith
7/7/2018 - 4:31 AM

## Find length of loop in linked list

We know that Floyd’s Cycle detection algorithm terminates when fast and slow pointers meet at a common point. We also know that this common point is one of the loop nodes. We store the address of this in a pointer variable say ptr2. Then we start from the head of the Linked List and check for nodes one by one if they are reachable from ptr2. When we find a node that is reachable, we know that this node is the starting node of the loop in Linked List and we can get pointer to the previous of this node.

``````//https://www.geeksforgeeks.org/find-length-of-loop-in-linked-list/
#include<iostream>
#include<list>
using namespace std;

int data;
};
typedef struct linked_list node;

node* insert(node* head, int n) {
node* list = (node*)malloc(sizeof(node*));
list->data=n;
}

int CountLoop (node* n) {
int len = 1;
node* temp = n;
while (temp->next != n){
len++;
temp = temp->next;
}
return len;
}

int DetectLoop (node* head) {
while (slow && fast && fast->next) {
slow = slow->next;
fast = fast->next->next;

if (slow == fast)
return CountLoop (slow);
}
}

int main() {
int n;
node* head = NULL;
while (true) {
cout<< "Enter the element, enter -9 to stop: ";
cin>>n;
if (n==-9)
break;
else