Linked List Cycle

LeetCode: https://leetcode.com/problems/linked-list-cycle/

Given head, determine if the linked list has a cycle in it.

Use fast and slow pointers (Floyd's cycle detection).

1def hasCycle(head: Optional[ListNode]) -> bool:
2    slow = head
3    fast = head
4    
5    while fast and fast.next:
6        slow = slow.next
7        fast = fast.next.next
8        if slow == fast:
9            return True
10    
11    return False

Merge Two Sorted Lists

Design Singly Linked List

slow

fast

-4

cycleTo=1

Step 1 / 4

Step 1:

Initialize slow and fast at head. Tail points back to index 1.

Pointers: fast=0, slow=0

Focus: select @ [0]

cycleTo=1