Medium

21. Linked List cycle detection - Tortoise and Hare Algorithm

Objective: In a given linked list, check whether it contains the loop in it, if yes then find the Loop length and break the loop.

Loop in a linked list means the last node does not point to the null, instead it points to some node in the list.

```Input: A Linked List
Output: Linked list contains loop or not, if yes its length and linked list after breaking the loop.```

Example:

```Input : -10-20-30-40-50-60-30-40-50-60-30-40-50-60-30

here you can see that 30-40-50-60 are repeating ,that means it has a loop
```

Approach:

• Find the Loop
• Take two pointers, both starts from head
• Move one pointer with normal speed and another with double speed (tortoise and hare)
• If both pointers meets at some point, we have found the loop
• find the loop length
• At the point where both pointers have met, stop one pointer and keep moving the another one
• When another pointer meets the first pointer, stop.
• Keep counting number of hops, that will the loop length
• break the loop
• Move one pointer by the loop length
• Now move both pointers with normal speed.
• When secondpointer.next = first pointer, set secondpinter.next=null.

Output:

```  -10-20-30-40-50-30-40-50-30-40-50-30-40-50-30

Loop length is 2
Loop started at 50
Loop breaks

-10-20-30-40-50
```