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LoopInLinkedList
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LoopInLinkedList
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#include<bits/stdc++.h>
using namespace std;
class node {
public:
int data;
node *next;
node(int data) {
this -> data = data;
next = NULL;
}
};
node *input_data() {
int data;
cin >> data;
node *head = NULL;
node *tail = NULL;
while(data != -1) {
node *newNode = new node(data);
if(head == NULL) {
head = newNode;
tail = newNode;
} else {
tail -> next = newNode;
tail = newNode;
}
cin >> data;
}
return head;
}
// this algorithm is taking extra time =>
/* bool detectLoop(node *head) {
if(head == NULL) {
return false;
}
// head -> next -> next = head -> next; For checking loop detection
map<node *, bool> visited;
node *temp = head;
while(temp != NULL) {
if(visited[temp] == true) {
return true;
}
visited[temp] = true;
temp = temp -> next;
}
return false;
} */
// Floyd Loop detection algorithm (uses the concept of slow and fast pointers)
node *detectLoop(node *head) {
if(head == NULL) {
return NULL;
}
// else using the slow and fast pointers
node *slow = head;
node *fast = head;
// head -> next -> next = head -> next;
while(slow != NULL && fast != NULL) {
fast = fast -> next;
if(fast -> next != NULL) {
fast = fast -> next;
}
slow = slow -> next;
if(slow == fast) {
cout << "present at " << slow -> data;
return slow;
}
}
return NULL;
}
void print(node *head) {
node *temp = head;
while(temp != NULL) {
cout << temp -> data << " ";
temp = temp -> next;
} cout << endl;
}
int main() {
node *head = input_data();
print(head);
if(detectLoop(head) != NULL) {
cout << "Loop detected" << endl;
} else {
cout << "Loop not detected" << endl;
}
}