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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.
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
- 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.
-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