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Detect loop in linked list.cpp
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Detect loop in linked list.cpp
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/*Detect Loop in linked list*/
/*Solution : This problem can be solved without hashmap by modifying the linked list data structure.
Approach: This solution requires modifications to the basic linked list data structure.
Have a visited flag with each node.
Traverse the linked list and keep marking visited nodes.
If you see a visited node again then there is a loop. This solution works in O(n) but requires additional information with each node.
A variation of this solution that doesn’t require modification to basic data structure can be implemented using a hash, just store the addresses of visited nodes in a hash and if you see an address that already exists in hash then there is a loop.*/
// C++ program to detect loop in a linked list
#include <bits/stdc++.h>
using namespace std;
/* Link list node */
struct Node {
int data;
struct Node* next;
int flag;
};
void push(struct Node** head_ref, int new_data)
{
/* allocate node */
struct Node* new_node = new Node;
/* put in the data */
new_node->data = new_data;
new_node->flag = 0;
/* link the old list off the new node */
new_node->next = (*head_ref);
/* move the head to point to the new node */
(*head_ref) = new_node;
}
// Returns true if there is a loop in linked list
// else returns false.
bool detectLoop(struct Node* h)
{
while (h != NULL) {
// If this node is already traverse
// it means there is a cycle
// (Because you we encountering the
// node for the second time).
if (h->flag == 1)
return true;
// If we are seeing the node for
// the first time, mark its flag as 1
h->flag = 1;
h = h->next;
}
return false;
}
/* Driver program to test above function*/
int main()
{
/* Start with the empty list */
struct Node* head = NULL;
push(&head, 21);
push(&head, 4);
push(&head, 15);
push(&head, 11);
/* Create a loop for testing */
head->next->next->next->next = head;
if (detectLoop(head))
cout << "Loop found";
else
cout << "No Loop";
return 0;
}
// This code is contributed by Geetanjali